Head of Household

I am 74 and retired. I am the grandmother and guardian of my 16 year old granddaughter who has lived with me since she was 6 MONTHS old, full time.  I fully support her. She does not work and is a full time high school student.  Why is the new 2024 program telling me that I cannot file as Head of Household and must file as Single?  When it brings over her information from 2023 it does not fill in her "Status".