Twice a day with toothpaste. Also, take her along to the dentist next time you go, to register her if nothing else. It will get her used to the environment and you get double check with dentist about flouride in the water in your area which will help you choose which toothpaste to buy.
We've used Macleans Milk Teeth from when ours had their first teeth, just a smidgeon on a brush to begin with. Boots do one which conatisn Xylitol which apparently helps avoid ear infections, and we had one tube and while using it ours didn't have any - coincidence?
Mine went to the dentist whenever we had a check up from an early age, intially just for familiarisation and a tooth count but then progressed to a quick ride in the chair, on my lap then on their own, and a closer look.
if you can find an nhs dentist that is registering new parents which is a rarity these days do it asap, i usually see children from 2 years upwards to get them used to seeing a dentist and to catch anything early, (a child can be registered at birth but are only offficailly registered once they are seen) before 2 there is no benefit to being seen the only situation this is different is if there is an emergency (hopefully that would never happen, but if your child has a fall etc you don't wnat the hassle of trying to find someone to see them you want to be able to phone your dentist and be seen asap)
you should NOT use normal toothpaste for a small child because really it shouldn't be swallowed .. a very very minute amount will not harm especially if child is a good spitter but I would switch to one of the specially made for under 7s (like macleans) because it won't matter too much if they swallow it