She gets angry when she imagines I'm hurt

Yesterday, I experienced some small setbacks. My wife had decided to call out sick from work due to headaches. My second-guessing nature right now has me worried it was due to feeling unhappy instead. Nothing I could do about that so I went on with my day,  occasionally messaging to check on her or ask if she'd like me to bring anything for her on my way home after work.  By her posts, I could tell she spent most her day on Facebook. She had posted a message to her brother asking if he wanted to see a certain movie with her when it came out. I was not included by a tag but I guess I could still see the post. She also played a prank on her page tricking people into thinking she had a stalker and when they clicked a link it took them to the suspected stalker' page... theirs. When I got home I checked on her and then proceeded to fix dinner and help the kids with homework.  She and I watched some shows together.  I asked her if she wanted to go with me to a concert coming in May. She said she was not interested. I said okay,  but she imagined she saw disappointment.  I was disappointed but I thought I was hiding it. She got angry. "What is wrong?" she demanded. "Why are you acting that way? You need to tell me! You are hiding things from me and that is not being honest!" I admitted I was disappointed but it is fine and understandable that I would be. She settled down and we continued to watch. Later I asked about the movie and not knowing much about Facebook asked if I was invited and just didn't see that I was. How stupid.  Why did I do that? Anyway, she got angry again that it would bother me that she wanted to go with her brother. I explained I was fine with that I just didn't know. She settled again. Finally she was looking at her phone chuckling and since she always shares funny videos with me I asked what was funny. She explained that an old guy friend of hers did not open the prank link about the stalker,  but instead messaged her directly. She believed he was indicating he would come kick the stalker's ass to protect her. I did not feel it is appropriate for a guy to feel he needed to protect another man's wife but thought I was hiding my feelings. Again she somehow perceived I was feeling something and became angry. I explained I did not feel he was being appropriate but she still believed I was behaving badly. 
 
So something is wrong. Why is my wife so quick to believe I am reacting badly and then becoming angry about it? If she thought I was hurt,  why can't that instill feelings of concern instead of resentment? 
 
I gave her nightly full body massage and she told me she had decided to go to the concert with me. I told her I understood and she didn't have to,  but she seemed sincere when she said she wanted to and thought we'd have a good time. I'm still very confused and very concerned. Not knowing how she is truly feeling and what might be motivating her is killing me. She is having dinner with a girlfriend tonight. This friend is one who my wife has kept up to date with everything going on in our recent marriage difficulties. I'm so worried her unpredictable volatile nature was somehow due to what she was planning on talking about with this friend.