Your daughter can file as "Head of Household" if the following is true:
- She was unmarried as of December 31, 2016 and
- She paid more than half the cost to run her home in 2016 (rent, utilities, etc.) and
- Supported a qualifying person.
Based on your question it sounds like #1 She was unmarried and #3 she supported her child, a qualifying person. If that is the case and her answer to the question "Did you pay more than half the cost to keep up your home in 2016?" is true, then she would qualify.
More information:
https://ttlc.intuit.com/replies/3288637
https://ttlc.intuit.com/replies/5649840
