Future MIL

So this ongoing saga continues. She’s stolen thousands of dollars from my fiancé, she’s said horrible things about me and my family whom she’s never met, she’s made snide remarks to me, she drinks a fifth a day. TODAY she posted on Facebook that she can’t wait to be a grandma and prays she will be one soon. I have been sick to my stomach and shaking and in tears upset about this. My fiancé is her only son so I’m her only option to become a grandma. I am 20, make shit money, live at home, still getting my education, and we aren’t even married yet. The fact that she would put this much pressure on me and PUBLICLY is so upsetting and abnormal to me. All these things are adding up and have me in serious question of my relationship, wondering if it’s worth this. I’ve put up with so much already and I’ve kept my mouth shut about all of it. I don’t know what to do anymore. Is it weird that she would post that publicly to Facebook when she knows that her son and I are in no position to even THINK about having kids right now?