My fiancés ex girlfriend is saying she is pregnant, she has had 6 kids and had her tubes tied. I don't know rather to believe her or not. She stated that her obgyn said she only has a 20 - 30% chance of carrying the baby? Yet don't you all do an ultrasound to see how the baby is and if it is in the tube since they are tied? She said she has a sonogram but hasn't showed us yet? I'm just curious on how likely this is.

In one large study, 143 out of 10,000 women got pregnant after a tubal. That's very low. Some tubals are better than others.
I don't see what having a tubal would have to do with the odds of survival. If any of this story is true, I would think there are other factors.
Wait and see and try to stay out of it for now. Let your fiancé deal with proof if this is an effort to involve him.