Unfortunately I can't see the pic.
Tie mom up to something solid and love on baby right next to her. She isn't being aggressive but she's being a mom. She just needs to learn that she's not allowed to interfere with you and your hubby. If you fix it so she can't get between you and baby a few times, she'll probably calm down and get used to it. Most mares are pretty protective the first couple of weeks and then mellow out some. My husband calls it "the new wore off", they seem to be less and less concerned as the baby gets older. But, of course, if you wait til mom doesn't care, you end up with a little wild heathen on your hands.