A:
Masturbation is very normal at this age. Children discover it, and discover that it feels good. Its hard to blame a kid for doing something that feels good.
However, its perfectly fine to put limits on it. You dont want to make her feel bad or shameful for doing something normal, but its okay to discourage her from doing it in public. Explain that what shes doing is fine, but that its a private thing she should do in her room.
If your daughter has delayed language skills or other developmental or behavioral problems, talk to her doctor. In these cases, the masturbation can be part of a bigger issue. If not, dont worry about it. With some gentle guidance from you, this phase will pass.