Hi Kristen. There's a number of answers here.
Expose her as much as you can to other horses.
Work her every day. Do you do much ground work with her and how switched on to you is she when you are handling her?
She needs to learn to rely on you to make her feel safe and the only way you can do that is by becoming her leader.
Have a blood work up to make sure she is not lacking/suffering from anything.
She may be lacking in Vit, B and it can have a natural calming effect if supplemented with her feed.
Actually a think all of the above are probably the key.
Good luck with her. You both need to be having fun.

Tori had some good points. The best things to do are to expose your horse as much as possible to the "scary" things.
When you are in open space, just get off your horse and do some de-sensitization. Toss your reins or a mecate over the horses back, neck, rear and legs. That helps to calm them down if you are doing something relaxing that they are familiar with (If your horse has not done that before, teach her in your arena or her pen). Lungeing your horse when she is scared will only make her more jumpy I have learned.
Maybe all you need to do is put her into a small munch of horses to live for a little while, and she will get used to it. Then ride her around in that pen with the horses. That wouuld help a lot! :-)

I also agree with Tory and Emily. Adding one comment, when she gets tense and shaking, have her halt and just stand there and look at things. You yourself need to breathe really deep and relax so she too will breathe and relax. When she finally exhales deeply, then move forward again. It sounds silly but your breathing also effects the horse's perception of scary.

She pays attention most of the time to me, it's just mostly in stressful situations that she doesn't (like the open spaces). I do quite a bit of ground work with her. I take her for walks about once a week, I do obstacle courses with her, and lunging. The latter is what we do the most. I was going to make a vet appointment for her shots and teeth floated, so I'll look into him running a blood test on her as well. Thank you.

How is she in open spaces with another horse? Some horses are far calmer when they have a calm level headed buddy with them. If that's the case, that may be a good and safe way to help her...in addition to all of the other wonderful advice you've received so far Best wishes!

I agree with what everyone else has said.
It's not going to hurt her any if you put her on a calming supplement. Smartpak has a couple of them you could try.
If you contact their customer service department, they will sometimes send you a free sample for a month.

Everyone has some great advice for you Kristen. The buddy thing works wonders. Last year I bought a mare that had done arena work all her life. She is a doll but needed to learn to trust my choices about open spaces. We rode her with buddies who were sensable and were not bothered by things. She quickly learned from them there was nothing to be scared of. Even now though she is terrified of motorcycles, so when we hear one coming the other riders we ride with will box her in so she feels safe. She gets braver every day.
Another thing I have found that works well with her is I feel her starting to get upset I will start asking her for more attnetion....just simple exercises that bring her focus back on me like flexing at the poll, or trotting circles, serpentines ect. We have found the harder she has to work when she is being nervous the quicker she gets over it.
I had considered supplements and decided to try other ways first....one thing we also did with her was change her feed and get her into a bigger pasture. But if you do decide to do supplements...start at the reccomended level then wean her off it.

Kristen, what great advice and knowledge from alot of great horse owners. I, myself, have a rescue that I just got in March. She apparently is green broke at best. She doesn't know how to lunge and now that she is feeling the best that she has in a long time has started to "see" things in a different way. Chickens crossing the road cause us some issue, some cows in a pasture that were friendly almost put us in a ditch.. lawn movers are a nightmare... but I have taken her past these things and make her work through them. She gets nervous but realizes that I'm there to guide her. I'm glad she's feeling so good and eventually she will know that nothing will hurt her as long as we are together. Good luck..

I was thinking of taking her to the next gymkhana on July 8 to get her used to the environment. I was told that I can just take her, walk her around, and even ride in the arena at intermissions if I wanted. I am also going to ask my neighbor if her horse is okay with open spaces and I am going to see if we can ride together sometime to help calm my horse about them a little more.
Thank you all so much for the answers!