Tiffanie has left the group i have no idea why Chrystina wasn't there but Tiffanie wasn't supposed to be there and Chrystina was.

There were only three, but Chrystina was there for sure, maybe because she had similarities with Tiffanie, thats why you thought it was Chrystina who wasn't there.
But Tiffanie wasn't there because when they were going to make their next album Tiffanie was let go because they were heading to a new direction and they thought Tiffanie's voice was too urban so they let her go, You can check on her videos on Youtube.com to confirm.... go to her page "Tuffanie" and there is an video explaning her story.

I am sooo happy that it was not Chrystina but Tiffanie who you really not saw!! Tiffanie left Girlicious.. I am happy for that! They sound and look wayy better now! Tiffanie is a great dancer and singer but just not Girlicious enough for me! Her voice is too loud,she's bigger than the other girls and the other 3 are more beautiful.. That's my opion.. She also likes to fight and make drama(watch the show!)i think thats the real reason they kicked her out!