My mare was bad with her feet - her entire life. She would get better with work and was best with me, followed by a barn owner that trimmed her feet for a while. She always needed tranquilizer for other farriers, though.
Part of it was a trust issue - she grew to trust me and trust the barn owner since he fed/worked around her every day. He didn’t pick up her feet every day but when it was time to trim her feet, he knew to take his time and was patient.
A friend bought her originally and it took about 6 months to get the mare to pick up her feet. It was all about patience and repetition. She slowly worked her way down the legs with the John Lyons-esque pressure and retreat. In other words, rub to a certain part, step away and praise, do again until horse has no negative reaction, then rub hands a bit farther.
My mare always needed tranquilizer for shoes and needed tranquilizer for other farriers because she only saw them at the scary shoe trimming time and they tended to have less time/be less patient with her than barn owner.
She also got worse if you didn’t work with her. When I was gone for 4 months, she was worse when I came back - that did lessen with time. She DID get more sane as she aged, though never completely sane.
I’m not saying your horse will be like this, just that time and patience are key and be prepared to always have this as some sort of issue.