[name]Erica[/name] summed it up; the other choices make my brain hurt! Please just use [name]Finley[/name]! I wouldn’t use the nickname [name]Fin[/name] on a girl anyway, and, though understand the fish issue, I don’t think it will really be that big of a deal. Why not call her [name]LeLe[/name] (like [name]Lee[/name] [name]Lee[/name]) instead?
[name]Finley[/name] is best - If your only concern is that if she wants to shorten her name, [name]Fin[/name] is too short, then she can spell her nickname [name]Finn[/name]. Her full name doesn’t have to be spelled that way too - think of [name]Zachary[/name] and nn [name]Zack[/name], and a million other names where the nickname is exactly the same. This way, she’ll have a full name that is spelled correctly AND a cute nn option.