The IRS has a publication specific to Divorced and Separated parents. I am providing you a link: http://www.irs.gov/pub/irs-pdf/p504.pdf
On page 9, they explain the rules
regarding who claims a child. Divorce decrees are no longer taken into consideration by the IRS. According to the laws
regarding divorced and separated parents, the parent with whom the child spent more nights with is the custodial parent. The other parent is the noncustodial parent.
On page 11, under "Applying this special rule to divorced or separated parents", they discuss tax benefits that go to the custodial and noncustodial parent when the noncustodial parent claims the child's exemption.
To summarize: When the noncustodial parent claims the child's exemption, the noncustodial parent is allowed the exemption and the child tax credit only. The custodial parent is still allowed (if applicable) head of household filing status, earned income tax credit
, and the child and dependent care credit
The answer to your question is: She is the only person legally allowed to claim child care expenses. Since she did not pay all costs of child care, she really should only claim what she paid on her return. However, your husband might consider asking her to credit him for any refund she receives on expenses he has paid if he is willing.