Miss Hannigan suffered from severe depression.
And it shows. That's why she drinks and smokes heavily and is a mean foster parent to the orphans. She also has no friends or husband which is why she's hungry for men to be attracted to her.
shareShe's not a foster parent, she's the director of the orphanage. She's employed by the State of NY to run the facility--unlike a foster parent who is not paid to run a home.
That is why they call her 'Miss hannigan' and not mom.
yes she probably did suffer from something, But we need to remember that she is not a 'mom' or a 'parent' and she is doing this as an 'employee' and Warbuck's Secretary ---who comes to visit reminds her that she can go to the board of orphans and get her replaced if she does not allow specifically Annie to be adopted.