College brat angry at me over a seat?

I am in college and as I was walking into cl to my usual seat, a girl was in the process of pulling out the chair to sit in my seat. Normally I could care less but my friend sits right behind me. So I quickly spoke up and said "oh no honey, that's my seat." She listened and didn't sit but as she walked by me she was definitely pissed. She said very loudly "Oh I didn't know we had igned seats". Oh my God she took it totally the wrong way! I swear I didn't sound mean or condescending in my voice but I sure got on her bad side. She appears to be right out of high school, and definitely acts like it. She texts during cl, eats, drinks, talks rather loudly. She is blonde and slim but not very pretty but she acts like she is all that. Anyway, today in cl a guy asks her if he could sit in the seat behind her and she says very loudly (for my benefit) No you can't sit there! Oh I'm just kidding of course you can! My husband says that she is trying to set a trap for me so I would get into it more with her because she is mad that I let her know that she couldn't get her way. I'm 29 and I sooo don't want to deal with her so I keep my mouth shut and ignore her. I agree and don't want to make this bigger but she sure is trying. What would you all do in this situation?