I'm very sorry for your loss.
She may if she filed her late daughter's tax return. However, the back child support may cause an offset (i.e., if your late ex-wife has already been reported to the Bureau of the Fiscal Service (BFS), the IRS and/or state's Department of Revenue may take all or part of her refund if she was due one).
For more information: https://fiscal.treasury.gov/top/
