Yes, they will fill a baby tooth. Just explain to her everything that they need to do - even talk about using the drill. When I took 2 of mine to the dentist for the first time I prepped them and talked them through the whole thing. When we were sitting there waiting for him to come in and start, I showed them all the tools and told them what they are used for. Tell her that it will be noisy too - I think the noise of the drill scares them too. I used to be a dental nurse and the kids who were prepped by their parents first always coped better than those that just had it sprung on them. Telling them they will get a treat afterwards always helps too

And don't feel bad. Sometimes it just happens. Or you might be one of the lucky ones who has a kid with bad teeth. I have 2 kids with terrible teeth and no matter how often you brush them they still get holes in their teeth.