Well,
I would first get someone to speak to them, someone who is good at that and can diplomaticly avoid criticism or accusations. Maybe offer help in finding a new, well,
better place for the rabbit. An equally small cage in an overcrowded shelter without decent quarantine procedures, or being just killed, ahh, "euthanized" (here, I don't know of shelters that take in rabbits, apart from private enterprises that have their own problems).
Here, thanks to new "animal protection" laws only registered breeders and commercial enterprises are allowed to advertise pets on the internet now, so here most animals that overwhelm their owners, or when situations change, or someone is allergic, will face that situation, no way to find new homes. Have tried to get a neighbour sell his rabbits before that law, but it was too late. But, hey, it's animal protection as peolple with no clue or with financial interests seem fit.
Could not sell any either, all this years offspring is going to the freezer. Great new law.
The people really aren't approachable so I can't talk to them.
What's the worst that can happen? Ok, I reckon there are people who are difficult indeed, but well, after an approach not talking to you ever again wouldn't change much, right?
She sits at the front of the hutch looking so hopeful that someone will pay her attention.
That part is what you concieve, what your brain makes of what you see, not what the rabbit actually feels. I would avoid making such projections an argument.
Many stupid things are done for good intentions, a few years ago I had 3 girls show up at my door asking if one of the two "lost" dogs they caught was mine (it was normal in that area that the dogs roam quite free, no wildlife, no problem), one of the girls already bleeding from a bite..
Reporting them to authorities, well, I don't know the situation with those is where you live, but I would not do it without approching them first (or let someone who is better at that do it). Here, authorities are the rather big stick, I saw bad things caused by Righteous Blockwarts For The Just Cause, doing harm to people that had problems to begin with, and didn't actually do something terribly wrong....
Also that can easily be turned around and make my life hell. Bringing someone turn Blockwart on me is something I can definitly do without.
My approach is that people aren't that bad as one might fear, talking never harms as long as you are sure to stop before an argument gets serious.
Don't even think about stealing, ah, "rescueing" the rabbit illegaly.