C.G.
my daughter is doing the exact same thing right now. she does the pee pee dance so i say "let's go potty" and she yells no. then she'll go running a few minutes later.
basically for my daughters personality(stubborn/independent), decided to stop asking her. she'll go on her own. sometimes an accident. but i found when i asked her she held it more. i think it's a control issue for her. i wouldn't worry about it. the only other thing i can think of is if there is something stressful in their lives that is making it happen. but most of the time for us, it's that she is doing something that she doesn't want to stop. i think she thinks that if she goes inside to go potty that she won't be able to go back out or something. good luck and don't stress. i am sure she is fine.