As Iride commented, your really going to have to go slow. This is not just a new horse to you it's a New and Abused horse. That's a hole different kettle of fish.
Who knows how she was saddled up before or what she was asked to do.
Let her develop some trust in you, spending time just hanging out and doing some ground work will let her figure out your not going to hurt her.
We have a little SPCA pony who was badly abused by a couple of women. When we first brought her home she was terrified on me. She would follow hubby anywhere but wanted nothing to do with me. It took a good 6 months before she realized I wasn't going to beat the crap out her, now she's my little shadow. LOL