Spend some ground quality time with her. Brushing, just leading her around... Saddle her up, and just lead her out on the trail, or whever you would be riding her. Once you are both comfortable and breathing normally
, get up on her, sit in the saddle for a few minutes, then get off. Walk around some more, get back up, walk just a few steps, get off. Keep doing this until you can walk around a bit and relax. Then quit for the day. Next time start out the same, but extend the in saddle time. When you feel comfortable, do a little trotting, then back to a walk. Slowly increase in this way. If you even think she is going to buck, or if she is excited get off. Don't feel bad about it.
You want to feel comfortable, and relaxed around her, and she needs to feel the same way around you. Take your time, don't rush. If you get scared, get off and walk her. If you don't get back on today, ok, fine. If you just get up in the saddle, then get off, ok. Start at the beginning, and take baby steps. Starting this way, the steps will start out small, but it won't be long before they become big steps.
. You already know how, you just need to trust again.
Many people, feel that you have to push hard to overcome the fear. That works for some people, it didn't work for me. I just kept being afraid. The slow method was much more effective.
The idea with the horse is to have fun... Not fear, and not dread. When you get to the point where you don't want to ride, you need to back off, and get re-acquainted with the horse. Take your time. Only you know how fast or slow to go.
If she still bucks, try to figure out why? Pain? Colic? Bad teeth? Bad feet? Bad saddle fit? Sore back? Arthritis? Behavior problems, as in dominance issues, or just plain bad manners?... Try low sugar feeds, and maybe low startch feeds for a while and see if it helps her temperment.
Also you might see if you can ride someone else's horse for a few times until some of your confidence is back, then slowly work with your horse.