Do you think this mare is pregnant?

I work with the rescue horses and one of them was in very good shape. Now she's starting to get fat. A lot fatter than the other ten horses with her. She's not with any stallions just geldings. i know that's not good information, but do you think that the mare may be pregnant? Oh, she was pregnant about 2 years ago, but had a miscarriage. What are the signs of pregnant mares? Please help!!!!!!!