What's going on with her physical health? Take her to the vet for a check up because she may be in pain, or is feeling ill. She may be taking it out on you because in her world you are her god, and, in charge of everything.
Something else that comes to mind is, she may need a little refresher coarse on who's the boss around your household. Keep in mind that with some dog's having to show dominance is often something that must be done every day in everything you do.Taking over as pack leader when one is needed is something all dog's will try to do. It's simply in a dog's nature to attempt taking over as pack leader when the established pack leader weakens, (aging would be considered weakening in the dog's world). According to her thinking, the pack MUST have a leader! Fortunately, taking back the power is usually pretty easy. Just to straighten out the confusion of who's the leader of your pack, you may want to make a daily time for excercizes of simple commands like, sit, stay, etc...Make up some new commands, and tricks just to keep things interesting for the dog. It doesn't have to be anything particularly difficult, or involved. The simple act of you showing dominance may knock her back down to size!