My mom spends way to much time on the computer!?

Please help me. I went out of state for a month to stay with my dad and sister. I took a liking in guitar and I played a song to my mom on the phone and she cried telling me how much she missed me. Well I just came home a week ago and if my mom isn't working the first thing she does is get on the computer. I asked her if she wanted to watch a movie together and she was all like, 'No I'm playing my game" I asked if she wanted to play a board game or something and she said "No, I just want to play my game." I said, "Mom, I just got home. Why don't we do something together?" She told me, "I rather play my game so I don't stress." It has been like that for the past week. She never wants to talk to me, she never wants to do anything together. She just wants to sit around playing a stupid game online with a bunch of strangers. She was always pretty bad on the computer but it just got worse when I was gone for a month. She has 5 accounts on the one game and she isn't suppose to do that. The rules say it's only one account a person. So she's constantly going back and forth between all the accounts. I tried telling her how I feel. I even told her that she has a problem, that she shouldn't be on the computer so much but she snapped at me. When I try to tell her how I feel, that I want to spend time with her she tells me, "Oh boo hoo, stop tryin to pull the guilt trip on me!" It's really bad. she snaps at me all the time for no reason. When I'm gone for a couple hours she says she misses me but when I try to spend time with her she snaps at me. We barely said anything to eachother since I got back. It's stressful in my house. I felt so much better being up there with my dad but I know him and I would eventually go at it (Because he's an alcholic but lives with my sister in her house) I always had my sister and baby niece around so I ignored it when he was gone all night. Him and I don't have that great of a relationship so it didn't bother me when he stayed out all night but at least when he gets home we do stuff together. Like play the guitar, ride the motor cycle, watch movies, go out to eat, etc etc. My mom and I use to be close but she's being so weird lately. I don't know what to do.