[QuickSilver]

I would suggest starting small (and get some dog toothpaste, because you'll want to start brushing her teeth). Go at her pace.

When she is very relaxed, maybe when getting a belly rub, put a little toothpaste on the tip of your finger and hold it out in front of her. Let her lick it off. Each time, let your finger get closer until you are almost touching her lips. Then maybe get a small piece of jerky or something where she kind of has to bite at your fingers to get it. You can also try just quickly (and calmly) touching the side of her mouth while she is getting her belly rubbed.

I would be REALLY patient, like expect it to take a month. Just make a tiny bit of progress every day, and let her get comfortable. Then when you can start putting your fingers in her mouth, start rubbing a little bit of paste on one tooth at a time. After another month, you should be able to brush her teeth without protest.

Thor would struggle with every he had to escape the toothbrush, but by doing a little bit every day, he got used to it. I brush his teeth every night, and while he doesn't love it, he is very relaxed. He lies on his back and I give him little belly rubs after each side.