How do I handle problems with my sharer?

Hello. How do you know that she does not warm up? Are you there at the time? Could it be that she does not know how to warm up? Have you been through what you expect when she rides? Might she have misunderstood your instructions in some way?

Could you put the question like this?

"How do you usually warm up?"

My feeling is that direct questions, with no judgement attached, work best. Let her tell you how she thinks about warming up. From there you can meet in a conversation where you can explain how you see your horse's warm-up if her version differs.

If you still feel she is ignoring how you want things done, and you feel it is becoming harmful to the horse, you may have to end the sharer agreement. It is your horse, after all.

I hope that gives you a little more to work with.