If she looks young enough, just tell them she is a minor. No I.D required. Otherwise, just tell them she has no I.D. It is not the job of the TSA to figure out anything beyond that.
..Sadly, there are many posts on this board where TSA has taken it upon themselves to "figure out" a lot more from NO-ID flyers....be prepared for an inquisition and scrutiny of anything on her person....probably best for her to have no carryon whatsoever...no purse, no wallet...nothing.
As far as the minor thing...be VERY careful...lying to TSA could get you shackled....
TSA-Figuring Out Teowowists by Screwing Amerika.