Matalas said in an interview that Seven gave up before Janeway went full bat for her.
I guess that is his explanation. Frankly, Seven's Season 3 arc reeks of bad writing to me. I'm sorry, but it does. I can understand Janeway finally succeeding in getting her into Starfleet. But for her to reach the rank of Commander and become First Officer for the USS Titan in a little over a year simply strikes me as implausible. I can't help how I feel. This is like the Kelvin timeline in which Kirk was promoted to Captain of Starfleet's flag ship during his third year in the Academy. Technically, Seven should still be in Starfleet Academy.