They didn't reunite, yet. I think the current Gill with Su right now is one of the abandoned Gills that she received in the android repair shop. So while she is Gill, she isn't Su's Gill.
But she said "an android like me" referring to Anna gaining consciousness so it clearly is Gill, Su's Gill
I mean I doubt su can just give intelligence to any android just like that
I went to reread the last chapter of Vol. 1, and the current two chapters that features Su and Gill again. I suppose that is true.
MY GIRLS ARE BACK, we didn't get any backstory of them reuniting tho that's disappointing i hope we do