I haven't had an older dog before, so this may be completely odd advice, but I was wondering if there's something you can get to put under her belly or back legs that you might be able to lift her a little if she is have trouble walking? Something like this..
HandicappedPets.com - Dog Harnesses & Slings. Help Dogs Walk with Dog Lift Harness & Slings
So that when she does have some trouble you can give her a hand a bit better?