My DS got his first tooth at 12 months and its only been now that we have finally been successful in cleaning his teeth (He is 26 months).
We used to try to make it as fun as possible. We sang songs, we played games, we tried it in the bath, we tried it in the high chair, we used to give him a break from us trying and instead let him hold the toothbrush and was us do it. We had books, & a dvd, we tried stickers. We saw a dentist who said we just had to get it done somehow, we saw the community nurse who said not to force it and just keep trying and make sure he watched us.
Nothing worked, or if it did, it only lasted a short while.
I also posted on here and people suggested that I needed to force it and eventually he would accept it. At the time we did try it but it was sooo distressing for him and us (it took two of us and we were still not successful). He would thrash around, kick, violently shake his head, mouth closed tight. Sometimes he would scream and we could get the toothbrush in.
Fast forward to now at age 26 months, we are now having success (touch wood). It has been nearly two weeks and we are getting the job done. His teeth seem to look good with no probs.
We had enough of worrying about it and we made the decision to force it again. I figured it's better to put up with screaming etc, than to have him put under general anaesethic (sp) to pull out rotten teeth.
We wrapped him up in a towel (so it was harder for him to move his arms about) and he sat on my lap with me holding him firmly. My husband brushed his teeth (when his mouth was open from screaming). But at least this time we were successful. This went on for a few days. On the fourth day he said he was scared of the towel, so we put the towel next to us, put him on my lap and we reassured him it wouldn't hurt and daddy would clean his teeth softly. He struggled a little bit but he his sooo much better. He makes aaahhh and eeee noises (when he opens his mouth - very cute) and I stroke his head and tell him what a big boy he is and how clean and bright his teeth are. We still have the towel next to us which he uses to spit on (but for us - just in case he plays up again). We give him the toothbrush afterwards and he tries to clean his teeth too.
He even let me do it on my own the other day.
I'd suggest by trying to make it fun and where all else fails, try wrapping her up in a towel. Once she realises you mean business, she might give up and let you do it. Also be consistent.
Best of luck. I know how frustrating it can be.