Off the wall co-worker gets mad at me over telling two other co-workers people she's pregnant?

I work at Staples and we had an off day on Memorial Day and I was talking to this off the wall co-worker who was asking me stuff like is important and stuff like that. Then, she goes and tells our istant manager about what I said and asks him, making me a bit embarred (but because he's 26 he doesn't care and laughs it off). Then she tells me later that she's pregnant and then tell our other two co-workers when I was talking to them. Before anybody gets antsy, I'd like to tell you this is her third child so I don't even know what she's so pissed about. This girl seems to put her business out there so I have no idea why she's mad when you go and put your business out there to someone whose only been working there for 4 weeks. So I find out the next day she PMs me on facebook about how pissed she is at me for telling when it wasn't my place to tell anybody and its disrespectful and weird of me to do something of that nature. In any case she said there is no need for any further discussion and she told me to take it however way I like it. Now I'm annoyed that she PMed me on facebook instead of just confronting me in the break room or after work and just talk to me. Now my fiance scolded me for gossiping in the first place. Mind you, this girl puts her business out there so I umed the other co-workers knew what she was talking about. Part of me wants to apologize, but the way the facebook message tells me, I think I may just need to stay away from her. Also, her personality makes me also want to stay away because she seems to start becoming an instigator or she's not someone to hang around if you want to keep your job. What do you think?