My first thought is "how is she being a distraction?"
While the coach may not be equipped to handle her fast paced (probably sometimes manic) thinking, what s/he can do is give clear expectations and consistency.
Gymnastics is all about consistency, and what most kids with ADHD need is... consistency! And, a lot of patience. Personally (having a Spec. Ed. teaching background) I think ADHD is a bit over tossed around, and often mis-diagnosed. Many times, the students I had were not properly taught HOW to learn and what is expected, and they found ways to cope with a lack of structure, purpose, and eventually block themselves from being successful. There is a reason many many kids "outgrow" their ADHD - they simply learn how to cope better, and manage their own person.
It really depends on how your daughter is, and WHO she is. Is she distracting by doing things that are dangerous to herself and others? If so, she needs to be removed from the gym right then and there. It's a lesson. Don't do that, or you don't come back.
What's more likely is that she is verbally being annoying or distracting to other athletes. If this is the case, she needs to find a coping mechanism to deal with her need to verbalize her (pick problem - frustration, feeling of helplessness, feeling of inadequacy, etc.. whatever her flavor is), and instead she needs to find a productive action to move through the situation. Something that the coach is aware of - even if it's walking away for a minute to get a drink, balling her eyes out, and coming back.
Gymnastics is scary - and something that requires concentration. It's also fun, exhilarating, and full of positive emotion. I bet when she learned her first flip-flop, she didn't stop doing them - something that rquires a TON of concentration. I bet when she learns giants she will do the same. The problem is not that your daughter has ADHD, the problem is your daughter does not know how to connect to what she is doing. Why is she there? What motivates her? Why does she have problems and what triggers them? Sometimes, it's just the fact that she's sitting around, other times it's because there's too much blue on the carpet. She needs to find an activity that will help her refocus and maintain that desire to do better and not bring others down. The biggest problem for ANY young kid in gymnastics is learning HOW TO WATCH. Some people do not learn visually, they have to do. So, my suggestion for that is, when watching, ask her to "feel her muscles do what she is seeing." It's hard! But, it will give her something to focus on!
Also, is she aware of what she is doing? That's the big part of it. If she is aware, she has some control. How can you teach her to be aware? How can you help her identify poor actions and bolster good actions?
This is a discussion that can go on for hours. In reality, if your daughter is diagnosed with ADHD, and has that designation in school, then she is more than likely already receiving services through her school. Talk to her Occupation Therapist (does she have one? If not, is one available? Ask!), or anyone else who is helping her with the management aspect of academic and social skills. They can work with her on many personal skills, and they should be aware of her interests outside of school to help create a bond with her and see where she is coming from. It all works together, assuming your daughter's best interest is in mind.
As a final note: I would NOT in any way encourage splitting her meds. They are working for her for academics, and as much as I love gymnastics - they will be FAR FAR more valuable to her than any skill ever will. Making changes to medication without a doctor's approval will only lead to frustration and more problems in the long run. She needs to be weaned off meds like that, she cannot simply stop, or her brain will seek to find the therapy they were providing elsewhere.
When she is at gymnastics, she needs to know her expectations. She needs to have something to do. She needs to feel accomplished and have personal goals in mind. Help her. She will fight with you, and she will love you - but in the end, all the ups and downs you feel from all of it will only be a slight view of what she experienced going through it from her side. Be patient but firm, and she will be fine.