Crazy baby mommas?

My SO and I separated for about 2 months while I was deployed. He slept with another girl and they both Messaged me saying she's pregnant after me and my SO got back together and I moved across the country. I decided to stay with him but now it's 3 months later and she hasn't told us anything. She was very rude the one time we talked and now....nothing...she won't respond to us. What's a woman to do?