Isla is more of a redhead name than
Maeve. On the other hand
Maeve sounds better with
Finn and
Lars than
Isla does. Initials are more of a concern with characters than overall sounds I think? Readers are more likely to confuse David/Dave and
Dana than
Dave and
Maeve, at least imo. That the character comes from Maine is of little to no consequence either way imo. If
Isla is what has been working, I would stick with that.