At that age we used an oral B baby tooth brush (stage 1) and fluoride free toothpaste (just a bit, even less than pea size). The training toothpaste doesn't really help with cleaning, but it has an appealing taste that may make the struggle less hard.
If your child is cooperative you can sit across from her, have her open her mouth and gently brush.
If she isn't (mine was almost never at that age), lay her down with her head in your lap. She will probably scream, which is helpful since then her mouth will be open so go ahead and brush.
Tooth brushing is not optional in our house, I have terrible teeth and would like to avoid this for my daughter, so we did it screaming and yelling about 8 out of ten times... but it got better once she was a little older;)