Except even as an Instructor, she IS in active combat duty. This is the same rank she held in StrikerS, which we have every indication she holds due to preference, not any inability to perform. Even the post-StrikerS blurb that extolled Subaru as the "Silver Ace" or whatever it was still noted Nanoha as the "Ace of Aces". Yes, they've said multiple times that the untested Blaster technology puts a physical burden on her body, but if she'd been permanently crippled, even slightly, you can bet your bottom dollar Fate, Hayate and all the others who care about her would have brought it up by now. They certainly wouldn't be okay with her using that very same power in an exhibition match. So no, while the years may have taken their toll, there is no way they can sell me on "she's weaker because she's old now", especially after all the big deal they've made about her experience in the early chapters (remember the mock fight in the onsen, canonically less than six months ago? The one where basically all the juniors could do was watch the adults fight over them?) .