Child Support payments

My separation agreement calls for me to make a Child Support payment to my STBX, and for us to split extracurricular expenses and unreimbursed medical expenses. I am responsible for 2/3 of the extra expenses, and I incur most of the expenses. For the past 10 months, I’ve been compiling all of this every month, documenting everything in a spreadsheet, and calculating how much I owe her, which is always less than the amount of the Child Support payment.

Now she is demanding that I pay her one check for the Child Support and that we handle the other expenses in a separate calculation and separate check. Is this any legal requirement for me to do this?

You are required to pay child support and in this case you are required to pay the monthly support amount called for in your Agreement, the other expenses should be handled separately as that seems to be what the agreement requires.