Has she always done this, or is it a new behavior? And what do you do when this happens?
I cannot speak to an older dog, but when Jazzy was a puppy she would occasionally try to assert her authority over me with growls and bites.
I would {firmly, but gently} force her down to her side, and with one hand at her neck/shoulder and the other on her hip I would hold her. She would snarl and fight for a while {a surprisingly long while, and with amazing strength!!}, but as she calmed down I would talk to her in a soothing voice, then begin stroking her with the hand that was on her hip.
It wasn't a violent or forceful event, just making her calm herself down, but in a position that reminded her that I was in control – even when she was out of control.
We had maybe four of these little "episodes" before she stopped completely.
Now I can do anything to her, take anything from her and she doesn't make a peep. She just had to learn that she was not the top dog with the humans in the family. And she is a very sweet, loving, cuddly family member.
I won't tolerate any dog I own even growling at me, and esp. not at my kids.