i would actually love all of that? even more so if fiona was maybe oblivious to WHY marnie just seemed to hate her guts? fi's not an ambitious person, she's usually good about keeping to herself, but she has a sort of...chaotic good energy at times that's probably emphasized by the friends she keeps who are a little more outgoing than she is. i'd love if fi briefly dated this guy that marnie was really into and it kicked off this bizarre, one-sided rivalry that she was just like "well okay then, what a weird freak" about throughout middle/high school, if that works for you! it seems like they're both kind of going through it at the moment (marnie's husband dying, fi's mom being diagnosed with alzheimer's), so it would probably be a little poetic if they managed to befriend one another now?