If she's upset by that- then she's probably insecure. I use several trainers and if you really don't feel comfortable telling her that you like the others, just tell them that you've got a predetermined situation already. The more instructors, the more you learn so it's really better!I use 3 or 4 during the show season. A dressage, jumper/hunter, jumper and eventing. Because the eventing coach is most expensive and I really only go for pre-show tune ups. Then for jumper/hunter I go once per month and she gives me things to work on. The jumper Iget twice a week and also get to apprentice under her. My dressage I do anytime I want to because she stays at the barn.
You really are better off with more than one! I know I have an excessive amount but it's just because most of them I have arrangements that make lessons almost free!