Using 2 trainers

Also -

If you are just starting in eventing, the higher up trainers will not have the time to teach you the basics. They will have expectations of what you should already know.

The trainer at the lower levels can certainly teach you the foundation.

Thanks so much for all the great positive feedback. I'm really glad I've joined this forum!

I have a similar problem. My current trainer teaches hunt seat and jumping, and she's an incredible teacher. I would never go to anyone else for hunt seat. But I also want to get into dressage really really bad, and I know a good trainer for it. My hunter trainer would be extremely offended if I took lessons from someone else, though. It just wouldn't be a good situation.

I don't really know what to tell you. Maybe you could explain to her that she's the only trainer you'd want for the discipline she teaches, but you want to expand your skills.

I don't get it. It isn't like you signed a contract swearing an oath that you would never train under anyone but that one coach -
Do not lie though, I absolutely stand by that - be honest and put your heart on your sleeve.

Do not allow them to make the decision for you regardless - your money, your horse, your education. You are paying them for a service - nothing more, nothing less.