Lila is a better Fox than Alya, Alya should have a Miraculous that is related to investigating.
Rossi is resourceful, creative, mischievous and a natural lier. She messes up yet she knows how to cover herself. Even her job as an Akuma was incredibly well done (Volpina is still one of my fav Akuma battles). If she had the motivation (instead of being a villain worse than the villains of the show because As--/truc likes to demonize teenagers) and Trixx, she'd be one of the best heroes. I truly believe she's the most fit for the Fox.
Alya, on the other hand, is clever; but she isn't as tricky and shady as Lila is. She's a more sincere and direct person and has a flashy personality (Lila has a flashy persona, but she's still a shady person, there's a difference). I believe she's more of a simple illusionist than Lila, her lies/illusions aren't be as complicated as Lila's (or even Marinette's) . Alya, I think, fits better Miraculouses that allow her to be either quicker or detectivesque. Alya knows lots of things on how to investigate (aside from the shitty "Alya believes Lila", which I think forces Al to be ooc just to have drama), so a Kwami related to tracking or seeing the truth would fit her better as she's passionate and experienced about that. Maybe Alt!Peafowl!Alya (Alt!Peafowl: Peafowl having aura and intuition powers, seeing hidden things, auras, intention, etc) or Alt!Dog (one of my Dog theories: having tracking powers, via smell or via bonding with allies). She's not exactly a front liner but she isn't as aloof as I think the Fox should be. So I think either of these two options would allow her to be on her own while still fitting the teamwork mechanic, and she could use her signature ability: investigating.
Also imagine truth seeker Alya and lier Lila being a duo. Hating each other yet having to work together.