Why would anybody do that?

I just don't understand the situation with my stepmom. She still wont talk to me. I tried to fix things... no progress. She either ignores what I have to say, or comes back with something. I had to email her today for two reasons. First, I needed to request that she give me Dad's cell phone (which comes into use ONLY after he comes back from Iraq) and the home phone (so I can try to get in contact with the kids). My cell phone busted about a week ago and I lost all my phone numbers. Second, I had to tell her that Josh and I are engaged. I suppose if I didn't tell her, I would be making and even larger effort to push her out of my life. Whatever.
She actually responded this time. She wrote the phone numbers and "Congrats on your engagement." Thats it. Nothing else. What the hell compels her to be such a horrible person to me? I don't understand what it is that I've done to her. I don't deserve this. I am so tired of her treating me like this. Its not like it has only bewen going on just recently. She has been doing this to me ALL MY LIFE. She puts a permanent, long lasting guilt trip on me.
The other interesting news of the week has to do with my Dad. I sent him a long letter about 2 weeks or so ago telling him exactly how I feel about this whole Pam situation. She told me that I "wasn't welcom to visit when Dad comes home from Iraq," and that was the last straw for me. I felt as though she no longer had the power over me to tell me when I can and cannot visit my father. Fuck her. I said it, though, in the nicest way possible. I didn't want Dad to get too upset while he is over there. I didn't want to get him involved at all, but it went too far. So, I haven't recieved a response from him. I am not TOO worried about it, though. I understand the pressure he is under and don't want to push it. BUT... a couple days ago I sent him an email telling him Josh and I are engaged. I figured I would at least get a "WOW" or something from him. NOTHING. I sent him an email today saying that I miss him a TON and love him a TON and hoped that I hadn't pissed him off too much. I assume this is the reason for the delayed response.
Not sure what to do... I don't want to stress TOO much. I'll just have to be patient and wait it out. Its my Dad, though, you know? MY DAD.