I changed classes last week as I wasn't very happy with the first one - the C was too busy to tell but I told one of the people that help with the weigh in.
Went to new group tonight and guess who was helping with the WI?
This has happened to me, just smile and blame it on a change of work commitments / DH work commitments / kids after school commitments etc etc, then smile and say not sure if it will be one off or regular!
You dont have to justify the reason why you have decided to change classes Hun and she certainly should not make you feel that you have to.
As long as you are enjoying the new one, thats the main thing.