I think it depends on what kind of trust issues and what else is going on with the horse.
Does she have some food anxiety? You could be sure to always feed her at the exact same time every day. Give her small amounts of hay several times a day and be sure she knows you are the one bringing it. Establish a routine and stick with it.
I had one who I guess you could say had some trust issues. I took everything really slowly with him. The first week, I just went out to his pasture and gave him cookies. Then I gave him cookies while I had the halter. Then haltered him, gave him cookies, took the halter off, and left. Etc. Tiny steps with everything. He was a worrier, too, so I had to make sure he knew I wasn't going to ask more of him than he could reasonably give.
You have to spend time just getting to know your horse and learning what motivates her and where he comfort levels are. If you hang out near her in her pasture does that make her feel good? Or does it worry her? Does she enjoy being groomed? Does she like attention in general, or does she relax more if you give her more space?
Others may disagree, but to me, to win a horse's trust, you have to spend time getting to know them and then slowly building up to things at a pace they can handle. Be really aware of their body language at all times. Understand if something is too much for them and back off or slow down. Show them that you are fair. Then you can slowly start asking more and more of them.
I don't know if it will help you, but I was writing a little "story" from his point of view, of some of the stuff I did with him. You'd probably be interested in the second post and forward. https://www.horseforum.com/horse-sto...an-mom-811183/