I too have to agree with Katy. You're the interloper here, and you're the adult. Your stepdaughter is doing what teens do, just in spades because you came between her and her father.
I'd make a quick trip to the bookstore to find a book on relationships and how to change the dynamics of your family triangle. Once your response to her prodding changes, she'll change her actions or give up.
Let me give you an example... If I said it was a beautiful sunny day, my son would say it was overcast. If I said he looked nice today, he'd ask if I was saying he usually looked like crap. And so on, and so on. No matter what I said, we ended up in an argument... me trying to rationally explain my side, and him countering whatever I said. After reading some books, I learned (and OMG it was hard!) to say, "Ok, whatever." At first it drove him nuts, and he'd escalate his comments and actions. Two days later, he said "You're not going there anymore, are you?" Once he figured out that nothing he said/did was going to get more than "Ok, whatever" or "whatever you say" out of me, he quit picking fights.
Remember that as long as you allow her to provoke a response, she's in control.
Oh, and drop the Myspace postings. If you want to post a message to hubby, use private email, IM, or the phone. Myspace is really for kids.
Kathy, Bellville TX