people who don't believe Kiriona is actually Gideon either don't like character degradation or don't pay attention
Gideon explicitly says she is still not used to being called Kiriona. her jokes are largely the same. there are several moments in the books where she moves to assist Cam and later Paul before stopping herself. the "get in line tho big slut" in the epilogue is extremely Gideon
but most importantly, she is having a terrible time made worse by watching Nona inhabit Harrow's body (and Nona kissed her! for a second she thought it was Harrow and realising it wasn't must have been heartbreaking)
another thing I don't see people talk about is that the Wake revelation impacted Gideon. she believed her entire life that if no one loved or wanted her then at least her mother did, only to learn that's not the case actually and she was conceived for the sole purpose of being killed. Wake called her bomb!
Right—Gideon believed that her mother had diverted her life support to the bio-container she was in because she loved her. That was not the case. She was just too valuable to let die.