Debbie, I'd recommend to give her "portion of daily shots" every day. Start with very quiet clapping hands close enough to her and keep doing it until she relax, then give her a treat. Then start again - relax - treat, and so on. Then brush her and mess with her. Do it for couple days until she becomes comfortable with that, then do it little louder, and so on. The problem you have not gonna be solved in 1 day, or 2 days, or may be even several weeks. I don't think real trainer will help much either right away (it does takes lots of time - more for some horses, less for others) - you have to do the sounds as part of your daily routine with her. Just keep safe enough distance from her and do it ON GROUND, not in saddle. When she'll be comfortable on ground you can start training same thing in saddle. Good luck!