This is probably right by the rules, but I think focusing on the rules issue is missing the real problem, which is one of communication. Whether or not you knew whether the rules support this, a Togorian Elite Soldier almost certainly would know if this would be sufficient to protect the girl.
Without being there, it's a little hard to guess exactly how this went down, but I assume you made your intentions clear to the DM. The DM probably should have at least told you that that wasn't going to be enough — and maybe you could have talked about other possibilities.
Going out on a limb a bit, it sounds to me like the DM was planning for the girl to die in that scene with nothing you could do about it, and didn't adapt quickly when you had an idea to save her. Without time to think, the DM might have thought oh &#×*§+! I don't know how to handle the next bit if the girl survives... it's supposed to set this whole thing into motion and now it's going to be ruined!.
I know I've gotten into this situation before and made bad judgment calls. I had a scene where the big bad guy had complete advantage and the PCs were supposed to scope that out, learn weaknesses, retreat, think of a clever plan and get an advantage of their own. It was a whole setup for a showdown dual which was supposed to happen the next day. Didn't work out as I had thought in my mind; the players did something they thought was enough, I tried to warn that the situation was dangerous — right in the middle of the evil headquarters! — but they felt like it was time to act, so they attacked, and I had the bad guy pretty much insta-kill a PC. This was totally within the "rules", but also the wrong thing to do — I was just focusing on not having planned out where to go on that case, and on the whole session being ruined by my lack of planning. Instead, it was actually ruined even more.
It sounds to me like something similar might have happened here.
Then, it got into an argument about the technicalities of the rules rather than about the story. It's probably a good idea to change that. Have a conversation that begins: Hey, I was really disappointed about how that worked out for my character and the NPC. Can we pull back the curtain a little bit and talk about this "meta-game"? I felt like my character didn't have any agency in that situation....
This shouldn't be "I think you made the wrong call", just expressing your own disappointment, and then listening to what the DM has to say — again, from a higher level than either the rules or the events of the game itself.