Since on-air radio contests are very strictly regulated by the FCC and perhaps by individual states themselves (hence the lengthy disclaimers you always hear on these stations whenever they run a contest that involves large prizes), my guess is that she's going to win -- and rightfully so.
It's obviously a joke and she has absolutely no legal claims to the remuneration.
Using your reasoning, any company can run a promotion, contest, or sweepstakes, and then get out of giving away the actual grand prize by substituting it with a gag or fake prize. What if you won the lottery in your state and when you go down to pick up the $5 million in real money that you thought you had won, they hand you $5 million in Monopoly money and tell you that the lottery was just a joke. I guess you'd just have to laugh it off, right? Or what if you won a contest in which the grand prize was promoted as being a brand new Ferrari. When you go down to pick up your new car, they hand you a Hot Wheels toy instead and tell you that the contest was just a joke. I guess you'd just have to laugh it off, right?
For once, I sympathize with the person doing the suing. I think this stunt is cruel. Radio stations often do give out cash prizes and I understand why the woman thought she'd be getting $100,000. Why is dashing peoples' (reasonable) hopes amusing?