What Can Be Cause For The Discomfort In The Vagina?

My four year old granddaughter spends a lot of time moving around and grabbing her crouch like she has to potty. She has been doing this for a very long time I've asked her so many times if she has to use the bathroom and she will tell me no. Now that she is older she has begun to tell me that she is only "getting the bubble to go away" in her vaginial area. What would cause that kind of sensation in that area?