Log into the Administrator account then change your granddaughters password or delete the account. Go into the guest account and remove any password.
My great granddaughter got on my pc and set up an account (she does not know what) however when you load it you have a choice to login on her account (she has no idea what she used as a password) or as a guest. Under guest you can not do anything, Please help.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic