Where do I stand with CSA?

im enquiring on behalf of my partner. He has a three year old girl who spends 4 nights a week with us or three with us and one with his parents. His daughters monther is now asking for child maintenance however we have her more than she does?

where do we stand as when calculated it says we should be paying her £20 per week even though we provided all her clothing, school uniforms, shoes, food entertainment ect for four days a week/nights a week.\ she claims the tax credit and child support we have no help in financially raising her.

I just want some clarification on where we stand.