We started getting our daughter to brush her teeth by letting her push the brush around in her mouth. Once she'd had a chance to do it herself, she was much more willing to let us brush them well.
My daughter screamed and fought about brushing teeth forever. We started about when she was 15 mo, and she is 3 years old now. She still doesn't want to do it. She used to scream all the time too. I guess its just persistence. I used to feel the same way you do now, though. It was so frustrating. It does get easier! Hang in there. You are probably not hurting her! You are doing the best for her.
Teeth brushing is just one of those HUGE obstacles daily/nightly of child developement isnt it! And it can be SO frustrating. One thing I want to add is it always helped my son when I told him/talked about what we were going to do and gave him options. "After we eat breakfast we are going to brush our teeth." Then talk about it on the way to do it. Then I'd ask "Do you want to brush your teeth or do you want Mommy to do it?" This gives him options and he responds really well to it. I know your daughter is younger so asking her that may not work but telling her what your doing and talking through the steps will remind her and help her know what to expect.
Also, you can always call a denist office and talk to someone there, they may tell you its normal or let you know if they think you should bring her in or not. If anything it will give you piece of mind!
Definitely give her a brush she can explore herself. That way it becomes familiar, not some weird object that gets crammed into her mouth every night. Try to make it a fun thing, if she's teething you may just want to back off for a little because its too painful. Just make sure shes not getting too much sugary foods during this time.
Love the electric tooth brushes too! Keep workin at it Momma! It's tough! She'll except it with consistancy sooner then later and it will become a much easier process. I know your pain!
Some children have very sensitive taste buds and brushing their teeth with a mint toothpaste is like brushing your own teeth with chili paste. Tom’s of Maine makes a kids toothpaste or use baking soda instead.