My friend wet herself....?

okay, so im 16 and i go to the car track alot with my friends...one of my friends dad built us 2 derby cars. Anyway, i got a new friend recently and she cant drive, as she is only 15, and she wanted to come to the track so i told her she can drive with me. We drift, and do donuts etc. and when i took a turn and started doing a drift...the first time she has ever been in a car doing that, she wet herself....now is is really really embaressed and i feel so bad, what should i do? she wants to come again this weekend, but she isnt sure what to do, and is still really uncomfortable around me and my older friends after what happen. How do i get her to be okay? and realize its not a big deal....thanks.