So, I think I might have fixed the problem (me and op are friends). It seemed to have allowed her to log in again, so I figured I'd share it on here for whoever is having problems.

Problem:
After selecting a character on the Character Select screen, the game will crash.

Solution: (note: I'm not sure which one of these was the fix, since we did both steps at once)
- Go into My Documents/My Games/.
- Delete any Final Fantasy XIV Beta folders.
- Go into My Documents/My Games/Final Fantasy XIV - A Realm Reborn.
- Delete all saved character data (this includes all FFXIV_CHARA_XX.dat files as well as the character folders FFXIV_CHR0040017A4D885C).

After that, try launching the game and hopefully it works.


Good luck.