As far as the feed goes, if she's eating that slow, and you have the option to, I'd put smaller portions of the hard feed into her stall more times during the day, that way less goes to waste, if she hasn't touched her latest serving, then you just don't add anymore. She should eat what she feels she needs to on her own, and since she's pregnant, take her time doing it, cause I'm sure she feels like a bloated whale at this point. Can't possibly be comfortable. Does she have free access to hay? If she does and has, then I wouldn't worry too much about her getting or not getting the right nutrients and vitamins. Most horses get plenty of what they need from hay alone, and that includes the horses in the wild who never have access to a grain bucket, and they are fine when they are pregnant. I would just make sure that she continues to look healthy and as happy as can be being pregnant, but make sure that she is getting plenty of hay every day.
She's going to be sweating more than normal at this point just because she is carrying all that extra weight around, and I don't know how much you've worked her since breeding her, but if she wasn't really fit to begin with, then she's going to be even more out of shape at this point, so she's going to get hotter quicker. She sounds like she's doing pretty good though. Looks good, still got a shiny coat, doesn't look like she's getting colds or anything. Definately post pictures when she foals though. We all are gonna wanna see baby pics.