Does she live really close to a motorway or high pollution area? I know some rabbit owners who won't let their buns have the local grass because of all the toxic stuff (don't agree with it, but their rabbits)!
I would say, as the weather improves, check them as often as you can for signs of flystrike best site I;ve found to explain it
Vet emergency stuff for rabbits is; not pooping, not eating or drinking, stomach making odd noises or feeling v.bloated, being v.lethargic, eyes going gunky, fever, convulsions, bloody nose discharge, difficulty breathing, sneezing (some rabbits sneeze around hay or if something tickles their nose, but if it 'sounds' like a cold or wet sneezes)
If you're anywhere near Leeds there has been a Myxi outbreak (discharge from eyes, swelling of head, eating,drinking & breathing looking difficult).
I think you've got the right idea cleaning out every few days, I've got 2 house rabbits who need changing every few days (even though they're only caged overnight).
Cucumber is a bad choice for daily feeding to (most) rabbits (because it's so wet, same with tomatoes, so check that rabbits poops aren't too wet), if they're having any problems with cucumber or any veg; better choices are things like parsley, spinach, any lettuce that isn't iceberg (again too wet)..but obv. if she's happy they're ok with their veg diet it's fine, just fyi-ing.
Hope your friend gets well soon, good luck bunny-ing!!