tampon use

okay..so my bestfriends birthday is on tuesday and we are going to a water park. we both got our periods on the same day and she has never used a tampon, but i have. our periods are supposed to end the day before her birthday or on that day. she is worried that there will be a chance that she will still have her period and she is freaking out about using a tampon. she thinks that it will hurt because it is only her first time, i told her not to be worried and that it wont hurt it will just have a weird feeling. anyone have advice on what else i should tell her?