Serenity, allow me to apologize for some of the less than civil post you have read.
You seem young and willing to learn. Its sad that others choose to ignore those qualities and only want to argue. Most adults have mature conversations not all but most.
I have lost a foal of my own and a couple from rescues. Nothing we could have done to prevent the loss. My foal was positioned wrong and it took to long to foal. The mare survived and had a very nice filly 2 years later.
The rescues probably lost their foals due to malnutrition.
It happens. That life. In the 53 years of my life my family and I have lost about 5 foals and never a mare.
You need to be prepared for the worst. Get the US, and ensure she is current on all her shots. Take every precaution you can. All that is good advice. Including getting the genetic test done.
I also think NDappy and Golden Horse want to help you avoid having to deal with the loss of an anticipated foal. Once again your young there is plenty of time for you to learn the hard lessons in life. Some not all can be avoided.
There is no need to worry the whole 11 months or more a mare carries a foal.
You will worry enough during foal watch.
If she is pregnant you have plenty of time to ask questions and become informed. Educate your self and feed that mare a good quality hay/ pasture and ration in her last trimester. Shalom