I couldn't immediately recall based on the angle in the screenshot, but from a frontal image and with the same type of clothing (i.e., bra and dress), it is definitely the reverend mother.....
Yeah, probably none that I am aware of ......I mean Zahra's are pretty big but not as big as the reverend mother's.....
But then again, (lore-wise) reverend mother's purpose is to essentially serve as a motherly concubine/baby-making machine of sorts as part of her high-ranking role in the temple so I guess it's sorta natural/expected that she has that kind of XXL mommy milk tits physique...
I'm sure she knows more than she is letting on, that's for sure... I mean, it is possible that the higher-ups in the religious sect of Zeta probably indoctrinated any of the new reverend mothers who were taking up that post. Because if I remember correctly, there may have been previous reverend mother's prior to the one we get introduced to in-game