Okay, so Cloud is a supersoldier, Red XIII is a magical creature, Cait Sith is a robot, Vincent has shapeshifting powers, and Aeris has magical Cetra shit. Why are Barret, Tifa, Yuffie, and especially Cid capable of fighting monsters and Sephiroth? Barret is effectively an ordinary dude with an exceptionally large gun, Tifa trained super hard but is otherwise an ordinary woman, Yuffie doesn't even train hard and is an ordinary girl, and Cid is literally a middle-aged man with nothing except a spear and an overwhelming hatred for everything.
Barret's black, Tifa has an impressive rack, Yuffie is a ninja and Cid is a mentor figure.
I don't think you've ever heard of anime, but all of the above satisfy the conditions for "worth keeping in the party."
The one where she has a dick and a pussy and gets sucked and fucked at the same time by a dozen Malboros, then gets mind broken and dies when the Malboro babies that she birthed eat her.
Maybe I read too much into it, but it sure sounds like she won't make it.
I think this is probably the best answer.
Thing is, everyone you mentioned was not super magical either. They were just normal people too. Aeris being cetra was incidental. She didn't know how to use the white materia, or even what being a cetra meant. It didn't gove her any fighting ability though. Just some kind of telepathy with other cetra.
I think you read into it too much. It says they feed off her secretions and not her flesh, and they won't get a reliable supply of secretions if they kill her. I'm not really into vore/nuff/guro, so maybe that's why it didn't occur to me to interpret it that way.
The Selphie one definitely eats her though, pity it's got a weak ending and pretty poor art.
Tifa was trained by the hardest dude in the land, Barret is fucking Mr. T with a gun arm, Yuffie is a Descendant of Ancient Shinobi Capital Letters and therefore arbitrarily powerful to the Japanese writers, and Cid is really fucking angry all the time.