C'est ta montre ? - Non, c'est ________ de ma mère.

Question

Why is "l'une" incorrect here? Maybe this logic is incorrect but I guessed that because you already have ce (c'est) in the sentence it would be repetitive to have another pronoun right after. I saw another question about it but am still confused in which contexts it is OK to use "l'un" and when to use "celle" and its other varieties

Céline Pickard · Accepted Answer

Bonjour chaos,
You will use "l'un.e de ..." when you want to express "one of ...":
C'est l'un de vous qui a cassé le miroir = [Lit: It is] One of you who broke the mirror
You will use "celui/celle/ceux/celles (of)..." when you want to express "the one(s) of ..." or "[somebody's]":
Cette montre ? C'est celle que tu m'a prêtée. = This watch? It is the one you lent me.
C'est ta voiture ? - Non, c'est celle de ma mère. = Is it your car? - No, it's my mother's.
I hope this is helpful.
Bonne journée !