I know it has been a while since the OP made this post, however, I wanted to add my 2 cents! lol. I have been in very similar situations. I think your husband gave you perfect advice. However, I know from experience, she just might try to act as if she cannot do it on her own, even if she can....especially if she's got her mind set to have someone else do it. She could "fake" you out so to speak. Just try not to ignore her. That will give her something to complain about. Advise her that you have bedridden patients who really need you and it would be in everyone's best interest if she puts the cream on. Remind her that she is there for help when NECESSARY. Also, remind her of "use it or loose it". Usually, when I remind them of how easily they could loose thier independence from laziness, they get the message quick.
I had a patient who was young, in her 40's and at our center for rehabilitation after major surgery. She could walk to the bathroom, shave her legs and she could apply her own hemroid cream....However, she would ring the bell after she was done using the bathroom because she wanted someone to wipe her! When I asked her why, she said "Well isn't that what your here for?"!!!!!