"She just had too much to drink," Heidi says, defending her sister in a scene from tonight's episode.
"That was not 'I'm having fun, I'm letting loose, I'm at this great event.' That was like some other problems going on in her life where she needed to get so drunk that she would black out."
Heidi, who's been house hunting with Spencer, hasn't witnessed her sister Holly drinking too much.
But Stephanie says, "Every time we go out, someone asks her to leave ... she really needs help, Heidi."
The Hills airs Tuesdays on MTV (10 p.m. EST). Watch a sneak peek of tonight's episode of The City!