$75 is pretty cheap, but the in-person exposure is worth $0, so what she is really selling is her ability to promote you online.
It's a novel idea, but really not terribly innovative, although I give her credit for making herself a business in a town that probably doesn't have a ton of employment opportunities for her. The hardest thing for her to overcome will be the fact that people tend to tune out paid shills like this.
She would be better off building up an online persona and name and then more gradually easing into this. OR, make the site "gangofgirlsinyourshirt.com". Sign up franchisees at top colleges across the US, and for $1000/day 50 hot girls promote your brand for the day.