Does anyone recognize this? A “what’s the title” book mystery

Last week, I was given “rabbit” as a micro-fiction prompt, along with the monthly theme “death and rebirth.” (Someone might be anticipating Easter?)
I don’t have a lot of experience with rabbits. I have seen wild ones now and then, and remember seeing a few for sale at the pet shop a long time ago. I’ve eaten a couple of chocolate bunnies. That’s about it.

So I struggled a bit to come up with a response to the prompt – I considered writing something about rabbits being chased, or people being chased like rabbits, but that seemed like it would go to places rather dark, and I didn’t want to do that at the time. I could also have written about the time I found a rabbit nest with babies and then crows attacked it, but that would also have been not that happy.

And suddenly I remembered a story I must of read several times as a kid, where a pet rabbit is found in the bottom of a coal scuttle or bin towards the end of the novel (I think.) It is, now that I think about it as an adult, a fairly disturbing little story, although it has a happy? ending.

(There was a time there where I’d whip through one or two younger young adult books in a day – and I’d end up re-reading some of them if they were kind of interesting and there.)

The problem is, I have not been able to find evidence the story I remember – which was either packaged as an older children’s book or a young adult book – exists. I don’t remember the title. I don’t remember the author. I have given the internet search engines different cues based on my memories, and the best that it’s come up with, is maybe I’m thinking of a now-apparently-out-of-print British novel from the 1980s. It might of been titled “Ros in Trouble,” according to the internet algorithms, which found one discussion of something that sounds fairly similar on Reddit. However, I would have sworn the main character’s name was something like Ellen or Helen, not Ros.

Maybe Ros is the name of the rabbit in the story?

It is entirely possible I’ve stuck plot points and characters from several books together accidentally in my memory.

Here is what I remember, maybe someone will read this and recognize it – please do let me know if you think you also know this book! The image of the rabbit being retrieved from the rubble towards the end – and how something about the situation in which it was found by the adults indicated to them that our hero was not alone in a cave-space in the rubble – is really strong.

Yes I said rubble. I am convinced the book was set in England, during the second world war.

The main character is a teenage (pre-teen? 13 or 14 years old?) girl who is living with both her parents, only her father is often away for some reason, she doesn’t get along with her mom, and they live in a sort of apartment building or rowhousing. I think they were either working class or lower-middle-class. The complex where they live has an old communal lavatory building, where heating coal is also stored. I believe her mother reminds our hero that when her pet rabbit gets a bit bigger, they’re going to eat the rabbit, it’s not supposed to be a pet, it’s supposed to be livestock.

There’s a woman who lives downstairs our hero (I’m going to call her Ellen) doesn’t like, and her best friend also lives nearby. Her mother has to go somewhere suddenly (maybe to a hospital because the father is hurt??) and Ellen is left alone for a couple of days, in the care of the woman downstairs.

Ellen and her friend learn that a German plane has been shot down nearby, and they go to see it. They learn that the pilot was killed but that it’s suspected other (others?) in the crew have escaped into the nearby woods. (It seems likely the plane was a bomber, but I don’t remember the detail of what kind of plane.) Ellen’s friend has an older brother who I think is in military service.

Ellen has problems with math homework, and the woman downstairs. Ellen declares that she’s quite capable of staying in her apartment by herself, thank you very much.
Later on, there’s an air raid while Ellen is in the lavatory building with her pet rabbit. And the next thing she knows she’s trapped in the rubble with an injured German from the plane.
I seem to recall that right before a bomb turns the building into rubble, the German first menaces her with a knife, next threatens to kill bunny rabbit, which he has captured, if she tells anyone he’s there and doesn’t bring him some food and stuff, and then at the last moment, tries to push Ellen out of the building ahead of him as it collapses.

Of course they’re trapped in a sort of cave space in the mostly-collapsed building together. Including the rabbit.
At first Ellen is pretty freaked out about this, but pretty quickly we’re building sympathy for the German. (I somewhat hesitate on this, but I’m fairly sure his name was Karl/Carl. Yes, that seems stereotypical, but this was a book written for children, and, some Germans have had to actually be named Carl, right?) Ellen figures he’s about the same age as her best friend’s older brother, maybe twenty or so, and I believe he says he has a sister name Elfrieda, which I remember because it struck me at the time as an ugly name – but also somewhat similar to Ellen. He cries when he learns his pilot-friend was killed, which surprises Ellen.

While they wait to be dug out of the rubble, and to take their minds off the threat that at any moment everything could collapse and crush them, Carl helps Ellen with her math homework. Because… of course he’s good at math, he’s German, and of course she for some reason happens to have her math homework with her. (Maybe there was a reason, but I don’t remember it.) (And yes, he conveniently speaks some English. And to be fair to the author, perhaps he was the flight crew’s navigator or something and had to be good at math for reasons beyond just being German, I don’t remember.)
Carl is fairly worried that if they survive getting out of the collapsed building, he’s going to be taken prisoner. Ellen tries to convince him that it won’t be bad, that the English will treat him fairly. He’s not convinced. (Also, while I’m pretty sure he’s bleeding in earlier scenes, as I recall he’s doing pretty well physically by the end of the story. He may have one of those dramatic ye olde artful arm injury you just stick in a sling and everything is cool again.)

Eventually adults on the outside dig a hole into the rubble and are able to pull Ellen out. Before she leaves, she promises to come back and bring Carl a jacket and some food and to help him escape.
I don’t remember if she just forgets her rabbit at this point, or what.
That night, she sneaks the jacket – I think it’s an old jacket of her father’s – and tells Carl about a rowboat he can steal and float down to the sea and try to cross the channel from there somehow. (I guess they’re near a river as well as a woods.)
I’m pretty sure there’s a scene about here when Carl sees the damage the air raid did to Ellen’s apartment building, and asks if anyone was killed. Then he wanders off into the night.
The next day, adults complete opening up the hole in the rubble, and discover Ellen’s pet rabbit in the coal bin or scuttle, and there’s something about what they find in there that makes them quite suspicious Ellen wasn’t alone in there, but it’s implied that they just kinda drop the question, because whoever it was was nice enough to Ellen.
There might also be something about how the nasty neighbour was accusing Ellen’s rabbit of eating the veggies in her garden, but we find out it was actually Carl. We also learn that the rowboat has gone missing, implying Carl makes good his escape.

So, does anyone recognize this book? Let me know!

Thinking about the story as an adult, it’s easy to see how this could be a scary story of kidnapping and psychological manipulation of a frightened, vulnerable minor at the hands of a radicalized warrior – but I’m pretty sure it was written instead as a somewhat scary story about two frightened, lonely young people from opposing nations discovering mutual humanity under dangerous circumstances. And solving math problems together.

Perhaps, as someone who had trouble with math at school, I was given this book in the first place because it has a hero who struggles with math, I believe specifically algebra, but then (with help) experiences an ah-ha math understanding moment? (I seem to recall Carl tells Helen to just ignore the letters? I’m not sure that’s right.)