[name_m]Hi[/name_m], my niece is [name_f]Sofia[/name_f], middle name [name_f]Belle[/name_f], and wants a nickname for high school. She says everyone has the name [name_f]Sofia[/name_f] (which may be an exaggeration) but I’m helping her find something else to go by in the fall.
She can’t decide between [name_f]Fia[/name_f] and [name_f]Belle[/name_f].
What do you think? [name_f]Fia[/name_f] or [name_f]Belle[/name_f]?
If she goes by [name_f]Sofia[/name_f] [name_f]Belle[/name_f], then [name_f]Belle[/name_f], but if she just goes by [name_f]Sofia[/name_f], then [name_f]Fia[/name_f].
I would chose [name_f]Belle[/name_f] as it’s a completely different name and doesn’t sound like the name “everyone has” but it’s her middle name so it’s not like she’s just making up a name out of the blue.
[name_m]How[/name_m] unique it feels might depend on how many Bellas/Isabellas/Arabellas there are around.
Another option could be [name_f]Zofie[/name_f]. 
[name_f]Fia[/name_f] or even [name_u]Fiadh[/name_u] is pretty too though.
She goes by [name_f]Sofia[/name_f]
While I love [name_f]Belle[/name_f], I think [name_f]Fia[/name_f] feels more natural in this case.