You don't owe her an explanation. You can email or phone, either way, and let her know that you won't be requiring her services anymore. Period. You can say that you wish to pursue a different training philosophy, but no explanation is needed. If she makes you overly worried about HER feelings being hurt, then she somehow managed to emotionally manipulate you in the process, completely unprofessional, and even more reason to move on.
Look at it this way: you are paying for a service, like your phone service or cable. If you decided that you didn't like the service you were getting and wanted to switch, would you be worried about hurting the cable company's feeling? Of course not. It is your money, and your dog, and your decision.
BH, OB1, TR1, AD
Rottweiler/Hairy Dog mix?? Shelter rescue
Gryffon Vom Wildhaus