Depends if you are paying per ride or per month. Per month, you probably wouldn't get any reduction as it all usually evens out in the end; this week they do a little less, but next week they do more. Per ride, no, you shouldn't be charged unless you or your horse require assistance during the clinic (warming up before the lesson, scheduling, stable help, ect)
If she is riding the horse in the clinic, you should be paying the clinician fees at minimum. Above that, it will depend on the trainer and the clinician. Some trainers will accept just having the clinic paid for if it means they get to ride a good horse with a clinician they respect, an opportunity they might not have otherwise. Other will want their regular fee or a reduced fee. Up to your trainer.