I always take it as a sign of love and not a sign of "ew mommy, you're dirty!" I just think Oliver knows that I've saved him from a street life and I'm the one that provides the food, the least he can give back is a little grooming
I think cats do it to all members of their 'family' as bonding, and to ensure that the family all smell the same as a sign of recognition. Many animals do the same. So it is a compliment - she thinks of you as belonging to her group.