Hi & welcome Lexus.
First & foremost, it's not fair to keep a horse alone. They need company. They commonly develop physical probs, as well as mental ones from being kept solitary. So I'd first organise to get her some company, and budget for having at least 2 paddock beasts on your 3 acres. Pref. another equine, but if you can't possibly manage that, horses are often happy kept with sheep or goats.
Depending on your climate & environment, setup, 3 acres may not be enough space for one animal, let alone more, if you want to avoid having it trashed, so I'd also consider looking at keeping your horse(s) elsewhere part time, to rest your property. Praps you can 'keep sweet' with the current barn & keep her there for the trail riding season!
• plan on fencing in about 1 3/4 acre total, divided in two parts, one portion 1 acre the other portion 3/4 acre. Plan on feeding hay twice a day and stalling during rainy weather to prevent the ground from being tore up from her hooves.
I suggest looking into track systems, aka 'paddock paradise'. Instead of fencing into blocks, & having a square, boring, sedentary 'sacrifice yard', you fence a narrow track around the border - this can be done as permanent fencing, or using just tread-in removable posts & hotwire, so you can chop & change, easily move areas to 'rotate' grazing. The advantages are; the horses are not permanently on most of the land, so it doesn't get trashed/overgrazed(or if too rich/much for them, they don't get so much); it encouraged exercise, especially if hay, water, hangout areas are spaced as far apart around the track as possible. Especially if there are a few horses on the track. Whereas horses kept in 'regular' type paddocks, esp if they're smaller, esp if there are only a couple of animals, tend to be sedentary; you can easily put down areas on the track of 'pea gravel', or logs for them to step over, or such, to make for better footing, specific exercise(lifting feet high over logs good for stifles for eg), etc.