This is a fun constraint to work with, honestly. The thing is—magic incompetence only feels like a cop-out if it's passive. If she's just bad at spells and that's treated like a weakness to work around, yeah, it gets stale. But if her avoidance of magic is actively creating problems she has to solve in other ways, that's way more interesting.
Like, what if there are moments where magic would legitimately save her life, and she can't use it—not because she's mechanically weak, but because she refuses? That's character conflict baked into every encounter. A mage throws a spell at her in chapter 8, she can't counter it with her own magic, so she has to improvise—dodge, use a shield, get creative with positioning. That's more interesting than just having another sword.
The other thing that helps: lean into why she avoids it. If it's just "mages suck," that gets boring. But if there's a specific, personal reason - maybe she watched magic go wrong in her family, or she associates it with loss, or she thinks relying on it makes you weak - then every time she's tempted to cast something, there's this internal pull. That's the story. Not the magic itself, but her relationship to it.
You could also have her pick up related skills that scratch the same itch without being spellcasting. Alchemy, for instance. Or enchanting. Those are still "magic" in the lore sense, but they don't require her to cast spells, so she's not betraying her character while still getting mechanical progression. She's learning to manipulate magic without being a mage.
What's the reason she avoids it, btw? That might help narrow down what would actually feel natural for her character.