A mare SHOULD protect the baby, and a maiden mare is more likely to be (over) protective and worried (which is problematic for milk too). Never tie her, or reprimand her for doing what nature is telling her to do. Halter and hold her, and handle the foal daily. Halter the baby (lots of changing sizes quickly), and handle it daily/pick up feet/etc), but have a handler hold the mom. This is important, but a horseman should be doing it NOW, (not for someone who does not know behaviors. Sounds like she has adapted easily and is being a good mom. For sure, the foal should be getting out asasp to move, cavort, etc.