I don't like her, so I'm incredibly biased, but I mean... compared to the plethora of characters within FF games that have gone through massively traumatic experiences, I would say she is not strong. I don't like Aeris either, but I can at least say that Aeris is an extremely strong character despite what has happened throughout her life. Terra cried about it, moped about it and even had to be convinced by everyone else to keep fighting. Hell, that didn't even work the first time. All the others carried on fighting without her, I'd say they were the strong ones. She did have moments of strength, but I would not say she was a naturally strong character.