First, I am sorry for your loss, Cheyenne. You ask an excellent question—but one that, unfortunately, we just don’t yet have the science to answer. Certainly, your horse has emotions, and she is likely to behave differently when she loses a foal, but we cannot say what it is that she might be thinking.
The best thing to do at this point is to help her move back into her normal daily routine as quickly as possible, and provide her with enrichment (such as a barrel with some treats inside, bobbing for apples in her water trough, etc.) to help reduce stress. Good luck!