I made an account to share some of my thoughts.. I'm aware this thread hasn't even been posted to since 2022, but I figured someone would still be looking into this still LOL. This will be a long and confusing post so bare with me.
Anyway, I wanted to bring up the possibility of Catherine not being "Sarah" OR "Aeris", but actually being the other person in the Sarah Saga who was Sarah's friend. The "something" person, "something" actually being the character name Sasarai. Catherine is cosplaying Sasarai in the photos of her that were posted, and I just haven't seen anyone point this out. We don't know which character "Sarah" was going by, but we know it wasn't Sasarai, since The Bishop Something was meant to be The Bishop Sasarai, the friend. I feel that when it comes to things like soulbonding that "casually" cosplaying a character probably isn't common. In other words, I think Catherine cosplaying Sasarai probably means she was actually Sasarai from the story, NOT "Sarah".
I also wanted to bring up the possibility of "Sarah" actually being Jen. Obviously Catherine isn't Jen, but we know she knew and was friends with Jenova and Hojo. IDK. Maybe that sounds crazy but it makes more sense to me than Catherine being Aeris. Never felt like Aeris was THAT crazy in Zack's accounts of her, seemed like she quit being friends with Jen and Hojo because they were to crazy. Seems weird for her to go off making up her own religion about soulbonding and what not after dropping Jen and Hojo for being to crazy about that stuff. Defintley seems like something more up Jenova's alley, and even with the way she acts in the accounts of the Sarah Saga.. reminds me of Jenova way more than anything Aeris ever did?
I think Catherine is a totally seperate person from Aeris.. I think Catherine is a friend of Jenova's and I think "Sarah" MAY actually be Jenova... Not sure if this has been brought up or debunked, but thought I'd share my theory anyway