I would only say you were in the wrong if she had had her bag up there already and just took it down for a second. It has happened to me in row 1 where I have put my bag up and realized I forgot to take out my phone or airpods or whatever. I pull out the bag for a couple of seconds to grab what I forgot and someone snipes the space. But when it happened, I just said to the guy that I had my bag there and was just grabbing something out of it and he moved his. When you are in row 1, you have no other choice. But if you got there first, fair game.