If she needs to use the toilet, you could teach her to say: "I have to go potty." "I need to go pee-pee." If you want to ask her if she needs to use the toilet, you can ask things like: "Do you need to go pee-pee?" "Isn't it about time you go potty?" "Why don't you try to go potty?" Usually in America, we use potty and pee-pee the same way. In British English, though, they usually say wee-wee instead of pee-pee.