If it doesn't have to be a rational reason, then with the car not working the air con wouldn't be either and she could get more and more hot and bothered and angry with her situation until she just snaps and rips her clothes off and up in a fit of pique. Once she's calmed down a bit, she'd of course realise the situation she's left herself in.
If you want a rational, thought out reason for taking off her clothes it's a little more difficult. I can think of a number of reasons for her to have removed her clothes but as for ripping them up... maybe she's not on a road, being on an off road section of the race; she needs to walk back to the road for help but the only way she can think of to mark her way back to the car is to rip pieces off her clothes and leave them as markers. Exactly how far she'd have to go and therefore 'how far she'd have to go' would be up to you.
Ideas freely given with no expectations of any kind, including compensation.