Thank you for your question
To deal with each point
1. Given that you paid for the bills and the food it is doubtful there was any profit - so no
2. You do not owe her anything - child maintenance cannot be backdated AND if the care is 50/50 it is not payable anyway
3. Water under the bridge given that you did not check and stop the payments!
I hope that this helps - please ask if you need further details
The fact that she receives the Child benefit will mean that you have to fight the CMS (CSA) to confirm that they will not make an assessment but eventually they will have to accept the position.
In any event it has nothing at all to do with the division of the equity