I had a bunny that would tooth grind under stress — When I had to handle her, when she would have to wait at the vets — it was her way to express stress rather than pain, and I had asked my vet about this as well (while we were at the vets) and she said it’s not uncommon for rabbits to grind due to stress.
However, if you normally handle her and she doesn’t grind her teeth, then this is still a new behavior. If the tooth grinding thing is really new for her, then I would watch closely. Put your ear to her tummy, when she is relaxing on the floor. Do you hear anything — a gentle periodic gurgling is what you want. (every 10 seconds or so). You could also try and do a little gentle tummy massage to help if there is any gas or other digestive issue. Sometimes just getting our bunny to run around a little bit can get the digestive system going (IF that is the problem) — grab some tunnels or things that will make her want to explore and see if that doesn’t help.
Regarding the greens, I have situations where Vivian will not eat a particular type,(one that she has always eaten before), and so it makes me wonder if I didn’t clean them well enough or if they just had a funky scent from where they were (before I bought them), or there was something wrong with them that I could not detect. Normally when I get a new batch of greens from the store, she will then eat them — so it makes me think that somehow something was up with the greens.
How have her poos been these last few days? When she flopped how was her breathing?