After you get her settled in, build her trust in you. Lead her all over, expose her to new things. When I had 8 or 9 babies every year, I led them through different parts of the trail courses I had set up. Mud puddles, cars, tractors, road graders, kids, dogs, blowing tarps (on the ground and on fences), anything you can think of that she would encounter, get her desensitized to it now. Get her to be a willing partner.
I prefer pasture raised horses, especially pastures that are not just flat stretches of grass. If they have hills and creeks and other things you might encounter on trail rides, that's even better. And fresh grass is great for growing babies, but get it tested if you can so that you can provide the nutrients she needs but that the grass lacks. Also, regular hoof care is very important for all horses, no matter their age.
These are the tips I can give you right now, but I'm tired and off to bed. Do you have any pictures of her?
Learning never stops