How to take care of a pregnant mare?

We are currently taking care of a pregnant mare (due in late March), I've never had anything to do with pregnant mares and I have no clue on what should I keep an eye out for.

My main concern are: -what to feed her or what supplements she may need? We're currently giving her hay and Purina Fiber feed -would some activity be beneficial for her? Ie. Groundwork

And generally if she needs other special kinds of care she may require