Maybe or maybe not!i remember the chapter were she was dreaming about a woman with black hair,she was teaching crista about a book..then when that woman was leaving she done something like erasing crista's memories of her or something..that's where I realized that maybe she's crista's real mother..that maybe she also have a Titan power but like eren she have an ability,like erasing people's memory or something!haha..this is just my hypothesis!
And about crista's personality she's the the kind of person who can betray people easily..it's like she will side when she think it's convenient for her!
SHIT! That last page at Chapter 61...I knew it! Christa's side is the real villain since they knew about the secret of the wall! I think Christa/Historia herself is actually a double spy too with her memories and all that...