I know you prefer the unexpected but I still love [name_u]Lou[/name_u] best as a nickname for [name_f]Louise[/name_f]/[name_f]Louisa[/name_f]. Otherwise I probably wouldn’t use the name [name_f]Louisa[/name_f] as the full name and would put something like Lua on the birth certificate instead.
I think [name_f]Lux[/name_f] is cool, chic and unexpected. Maybe [name_f]Louisa[/name_f] nn [name_u]Isa[/name_u], [name_u]Izzy[/name_u], [name_f]Lula[/name_f] or [name_f]Lulu[/name_f] would also suit.
All of these sound quite forced. I think most people will still shorten her name to [name_u]Lou[/name_u] or [name_m]Louie[/name_m], which is what happens to my cousin with the same name. These are sweet nicknames in and of themselves; if you really dislike them then I’d avoid [name_f]Louise[/name_f] altogether.