Kids do this all the time though your dd seems young to be doing it I would say "aww does it, you will be fine once we've changed you/ put you to bed/ had some sleep etc" and leave it at that, the more attention the more she will do it, letting her stay up was exactly what she wanted, it worked so now you will have to be very very tough in order for her to get the message you won't be played for a fool again!
I know you are worried she is really in pain but trust me as a mother YOU will KNOW when something isnt right, you will just know instantly. When dd2 fell off the toilet dp said oh shes fine and normally I'd pick her up give her a kiss and a rub and she'd go off playing but i INSTANTLY knew by the type of cry that my dd was in pain and the way she didn't just get down and play etc, you know her better than anyone and if she is really in pain/ ill you will know.