I also knew it was her due to her clearly being one of the more important members of the team but mysterious being absent for a lot of the stuff. I even think there was a scene before the reveal that shows her sitting alone in a room looking solemn right after the female titan failed her mission. Hmm...I wonder.
About my space chicken, she's either tier 8 or 9, so even if I wanted to add her here I couldn't. For one thing she can clench her butt checks to lay the eggs with such force that her normal egg would hit someone with enough force to do this:
Then she could make it even more dangerous by laying antimatter eggs, black hole eggs, nuclear eggs, etc.