You may not be up for this (which is OK), and others might disagree, but I would consider being perfectly honest with the trainer you are leaving. You could simply say that you feel like your training has plateaued and that you tried out a place closer to your college that seems to be helping you progress beyond 2 ft singles. Thank the coach for her time and everything she has taught you, and then don't look back.
I feel frustrated FOR you with coaches that fail to help their students progress, especially as the coach won't tell the student that it is time for the student to move on to a more advanced coach. Coaches need to hear from their students if/when they need to improve their coaching skills - or they will continue to loose dedicated students.
I agree with this approach. It may take some balls but it will benefit you and the trainer if they allow some self-introspection.
There's nothing like the Rockies in the springtime... Nothing like the freedom in the air... And there ain't nothing better than draggin calves to the fire and there's nothing like the smell of burning hair. -Brenn Hill