How do you 're-educate' an owner without causing offence?

I am fostering two lovely rabbits for a lady who is having to move house rather suddenly. She is hoping to find accomodation she can take them to but if not I will have to rehome them.

I know she loves her rabbits (she was in tears when she left) but, all though not dire, they were in need of attention when they got here.

Bertie, the male, had a very sticky bum and needs cleaning every day, his claws were very long (she did warn me of this) and I also noticed he has sore hock on his back leg. Maggie, is rather overweight and also needed a claw trim and both had a good brush too.

Im hoping to have them in full health by the time they go back to her (or rehome) but I want to make sure they stay that way. How can I politely point out that they need a better diet and regular grooming and checking over?

maybe you could make a leaflet and say your starting to issue these to all people you foster or rehome to?