They said it would not include any plotlines they already intruded. It wouldn't make for a great plot anyway. We already saw how she got injured. It wasn't a big boss battle or anything.
Yeah — it was stress, overwork, over-_training_, and a lucky shot. The drone's boss didn't get faced for years, and that's all in StrikerS already. There's human drama, great for doujin and fanfic, but nothing to build a Nanoha-style movie on.
To put it another way, the gimmick of Nanoha as a series is that magical girls are, effectively, Gundams. (She's the RX-78-2, Fate is Char piloting the Deathscythe.) And you don't make Gundam movies where the mech is down for repairs the whole time.