if my friend has been sentenced to 90 days can she qualify for house arrest?

Depends on the charges and criminal history. The Pre-Sentence Investigation yields a commitment recommendation called Pre-Sentence Report which details the case, and the offender's prior bad conduct (not just criminal, but civil misdeeds count against you, too). Ninety days is a cake walk, I remember when i had 90 days left on a 96 month sentence.