My suggestion is that you indicate by reply e-mail that the child will not need to be attending afterschool on Wednesday’s since it will not be necessary and this should end up resulting in less money your ex pays out. I could be wrong but since this is your custodial day it may be that you have a say for that one day…hopefully an attorney will answer. Keep records of all this for future reference
After you are married I do not believe that there is anything barring your wife from picking up the child since legally they will be family but it may be necessary to contact the school yourself.
I am sorry that your ex feels it necessary to make things more difficult for your child. The only person this is truly hurting is your child, though it is an inconvenience for you. Trust me when I say that if your ex is trying to keep your child and your fiancee from having a relationship, it will not work, especially if they have already become close. And that it will likely come back around on her. Just because a child likes the stepparent or even loves them, that does not dimish their feelings for their parent. The only things that dimishes their feelings is the parent’s actions and guilt over how they feel. Most parents have a hard time remembering this and end up putting the child in the middle.
My own stepsons went through this with thier mother. I do not doubt that they love their mother as much as they ever have, but they have seen her in a different light and they have thought a little less of her. They respected her a little less because of the way she acted towards me when me and my husband were dating. I still see the result of her actions over two years ago in the way they treat her. I can only tell you that with time, it does get easier.