Our 19 Year old horse is pregnant-and we're at a complete loss we have never had a foal before and need help!!?

Hello, We just found out that my 19 year old horse is pregnant after we thought that we had successfully separated the stallion and appariently we failed. My younger horse gave birth all by her self, and I'm afraid my older horse won't do so well. We're completely new with this whole foaling thing, what do we need to do? She is huge, and her "utters" are full of milk, but she's not waxy or dripping milk yet. Is there any way we can tell if she is going to give birth soon?? Please help us, what needs to be done???