That's garbage. Removal from the team because of one mishap? The coach is scared of having a diabetic on the team, probably because she doesn't know what to do in an emergency, and is looking for an excuse to not have to deal with it.
I agree with Joey, your daughter should have supplies in every bag she uses -- practice, school, purse, etc. I have Smarties and juice boxes strategically located everywnere my son goes, at the school, on the bus, in the daycare, in my purse, etc. But I assume this is a public school, yes? That being the case, the school is MANDATED to accommodate her by the Americans with Disabilities act. Do you have a 504 plan in place? If not, I would strongly suggest visiting the ADA's web page on 504 Plans to learn how to set one up — and the coach and the school nurse, as well as all teachers, must be included. Basically, anyone at the school who supervises your daughter must participate, and I say MUST because it is mandated by law that the schools accommodate her needs, and that includes extracurricular activities as well as academics. The law was written with the goal of ensuring that students with disabilities, and diabetes IS considered a disability under this law, can have access to all the perks students without disabilities have, within reason. But even if you DO have a 504 plan, it's clear that not everyone who needs to participate in it (meaning, the coach/athletics staff) has been brought into the loop, so you should call a meeting with the school administration to correct this omission. Part of the 504 Plan should be focused on how the school will accommodate her needs in athletics, and that DOES mean that the coach is to keep an emergency supply of juice/glucose tabs at all times. Coach has to keep a first aid kit anyway in case of injury, right? So, a glucagon shot and juice boxes can be added to that. It's really not that complicated, but it sounds as though the coach is scared to take responsibility for a diabetic child... and there's no need for that fear, so long as the coach knows what she needs to do and what supplies are required.
I would take this as an opportunity to educate and reassure the coach. Don't be confrontational. Be compassionate. Everyone who confronts this disease is scared of it at first, but if you can convince this coach to set aside her fears and put your daughter's needs as a person, rather than as a child with diabetes, ahead of her own need to be "safe", perhaps this can be resolved to the betterment of all involved.