I never heard of a pony division that allowed pro riders? But at any rate, I think better communication as to what to expect at a show would be a good thing all around. As far as the trainer bringing a horse to show in an open division for whatever reason, that’s normal and it’s fine, even if it’s just to get a year-end ribbon. That’s the trainer doing his or her job. No problem. But the first time this happened to us, it was disconcerting and a bit of a shock. There was no communication as to what to expect and I was paying a lot of money to travel to the show. I thought I was being taken advantage of (and I was on many other things but just not on this issue!).
However, you should also be aware that there are (I’m assuming even at a small show such as the one you describe) divisions your daughter should be entered in where she is just competing against her peers. These would include amateur hunter divisions for example based on academy classes or children’s or junior hunters that are just for kids under 18 and age group or any equitation division which by nature exclude trainers.
So it’s normal to compete against your trainer in open divisions which include warm up divisions and advanced events like hunter derbies or the performance hunters. But your kid should also be entered in divisions of her peers. Even the smallest shows usually have the latter.
I wish trainers would communicate all this to families so they would know what to expect on show day and therefore avoid hurt feelings, confusion etc. Showing is stressful enough and unfortunately you often have to learn through experience. Or ask the COTH forum!