Cat started swatting at my daughter recently?

My daughter is six and has always done just fine with our cats. We have 2 females (half-sisters) completely indoor cats. The cats have their own space and have always loved the kids in the past. She actually snuck up behind my daughter and deeply scratched her ankle while she was washing her hands. This scratch was very deep and bled for a while.

My daughter hasn't done anything to provoke her, but the swatter is the more dominant of our two cats. My four-year-old son does unnerve the cats a bit and is home more since he's not in school yet. He is actually rougher with the cats than his sister, but not mean, he's just a typical rough and tumble little boy, but the cat isn't swatting him.

She also hasn't swatted at my husband or I, so we can't figure out why my daughter is the target. The cat has never been like this before. She even hissed at the neighbor kids while we were out of town and they cat and dog sat. My daughter is the one who usually lets the dog out, but the dog and cats all like each other and really don't fight. This cat has always been skittish, but usually has just hidden if she didn't like something, now instead of running and hiding she is attacking.

We got both cats as kittens from my parents around 5 years ago, just a few weeks apart.

Any ideas or suggestions would be appreciated. If it doesn't quit we are planning to get a squirt bottle for my daughter when she is around the cats.