It's hard to put Fate's love for Nanoha into words. She'll do anything and everything for the other girl, and she's at her happiest when she's spending time with her. Like you said; they're soulmates. There's no other way to put it.

On a more serious note, she really wishes Nanoha could at least try to get along with Precia. >: She knows it's a tough thing to ask, and she's not expecting Nanoha to ever forgive her mother for what she's done, but... she really wants there to be as little hostility between her (and all her friends, raelly) and Precia as possible.