You mentioned before that she’s only about one. At that point, she probably can’t pronounce her name properly, and found the next best thing- [name_f]Fifi[/name_f]. Honestly, when she can get a grasp on the sound of [name_f]Ophelia[/name_f], [name_f]Fifi[/name_f] will probably turn into [name_f]Lia[/name_f] or [name_u]Philly[/name_u] or whatever she goes by. [name_f]Fifi[/name_f] won’t necessary dissapear, like it might become her "[name_f]Pet[/name_f]-Nickname-Only-Mum-And-Dad call her. [name_m]Don[/name_m]'t stress, okay?
I don’t know about you, but at that age my daughter would be obsessed with something for about a week and then forget about it and move on. I understand not liking her chose nickname, but tbh, I highly doubt it will stick. I say indulge her but also call her whatever you want. My daughter has about 6 nicknames, none of which have anything to do with her actual name. I’d say relax a bit, see if it passes, try something else to see what sticks but don’t stress about it.
A little bit more outside the box nicknames for [name_f]Ophelia[/name_f]:
Opie
[name_f]Opal[/name_f]
Filly
[name_u]Elia[/name_u]
[name_u]Lee[/name_u]
[name_f]Olia[/name_f]
[name_f]Lolo[/name_f]
[name_f]Leelee[/name_f]
It’s a bit of a stretch, but I like [name_f]Effie[/name_f]/[name_f]Effy[/name_f] as a NN for [name_f]Ophelia[/name_f]
I like Felly, and the suggestion of Faylie is my favorite. I would plan on using full name though
My sister had a friend [name_f]Ophelia[/name_f] and we called her Pheelie or phee.
Oh I love [name_f]Fia[/name_f] for you! I think it will age well too.
Hiya, I’ve never replied to a thread before but felt I should as my name is [name_f]Ophelia[/name_f] as well! 
I have always gone by Phely (feelee) but I sometimes get called Phe or Phel. My nickname has made me love my name more as it has helped me stand out and I don’t know anybody else who goes by it.
I know of a few [name_f]Fiona[/name_f]'s who go by Fi and so having the ‘ph’ spelling has made my nickname feel more exclusive to my name (if that makes sense?)
Personally, I don’t like [name_f]Fifi[/name_f] as I do think of it as more of a pet’s name and growing up it was used in a more patronising way…
Nicknames I like for [name_f]Ophelia[/name_f] -
Opie
Phely (obviously) Pheli / Phelie as alternative spellings
Phe
Phia - [name_f]Fia[/name_f] is v cute tho
Phel
[name_f]Lia[/name_f]
I know a young [name_f]Ophelia[/name_f] who goes by Opie a lot of the time.
Wow - honoured to hear from a real life grown-up [name_f]Ophelia[/name_f]! Your parents were avant-garde, haha! That is super helpful, along with all of the other great suggestions people have had. For me I think the “Ph” sound probably is key - but I like Phelie, Phia and [name_f]Pia[/name_f] and I’m going to try them out. Thank you!