Try IRS interactive tax assistant    https://www.irs.gov/help/ita/what-is-my-filing-status

or Do you have any reference guides like Quickfinder ?    There is a great flowchart to help determine HOH status.

This woman may fall into the "Qualifying Relative" category which allows your client to claim HOH.    Please do your due diligence and verify she meets all the necessary tests.

edit:  Sorry - she falls into "Qualifying Relative" category but that qualification type is not allowed for HOH status.      I should've taken my own advice and looked at the flowchart before adding the Qualifying Relative note.