Kudos for going back to school, I am in the same boat and I know looking for schools a second time around can be annoying/intimidating.
Schools with equine management programs that I know of.
Umass Amherst, Morrisville (SUNY), Mount Holyoke College, Mount Ida College and I think tufts, Michigan state, Purdue and possibly PennState. You might have to google around a bit, if the school has a agriculture element or an equestrian team. I don't know how many of them have online classes because usually riding or training is an element of course work. I also know most of the classes are business classes with some information on equine care. Key words that I would look for are equine management, equine studies or equine husbandry. I have heard good things about the Morrisville program; however, I have not been overly impressed by some of the graduates I have met.
The thing you have to remember is that as equine management you are most likely going to end up managing a barn. With that in mind finding barn help is really difficult and so you will end up cleaning a lot of stalls and do so often. Barn management is farming, which means its hard work, long hours and not much money. I just say this because I have seen a lot of people get into equine studies and then get disenchanted with what the job entails. I would recommend working at a barn or talking to a few local barn managers. That way you have an idea of where they went to school (Alumni contacts) and you can find out what they enjoy and what they find challenging about their job.