Speaking as someone with WEAK enamel and who's been on the receiving end of plenty of dental care, this sounds fishy to me. There are three options: your daughter has great teeth except one which has a legitimate recurring problem, but no one has explicitly said that to you or told you how to care for it, your daughter keeps having the same cavity filled over and over because its not being done right and again, no one is making that clear to you, or this dentist is over-treating or overbilling you for a problem that isn't really there. All of these, combined with the turnover, are enough to leave this practice or at least get a 2nd opinion.
Have you seen x-rays? Cavities and fillings should both be clearly visible, even to an untrained eye. You should be shown X-rays before any treatment every time and the problem and previous work should be pointed out and explained.
If they filled it white and insurance covered it in full, rather than at the silver level and you pay the difference, that tells me it was a front tooth (unless you have awesome, forward thinking dental insurance that always covers white fill in full)...if so, that's a lot of drilling into a pretty small tooth. I just had to get a crown on my molar after I got a third cavity and more drilling would have weakened the tooth too much. They weren't small cavities, but a third cavity in the same tooth, especially if its not a molar, is setting off alarm bells for me.
I think you should ask for a second opinion if at all possible, outside the practice. Ask around for recommendations...I don't know how insurance would treat a 2nd opinion visit so you may want to call about that. Good luck!