I've seen it once before, but I'm not sure it's a glitch... what kind of glitch would lead to a character model being placed in the CHURCH, of all places, which has no signifance after you escape from it with Aerith. You didn't even return (with the story, so to speak).

Also, when I saw it she was in the aisle and we didn't even need to take a step in order to for her to disappear, in a second she was gone, every time. We left and re-entered a few times to check, too.