"Who was she?" Ellie asks you, her typical nonchalance fading into a more jealous tone. She spent the whole day playing music with her band, and just when she got to the apartment a girl came out of there.

She has a right to know who it was, after all, you two live in the same apartment.

"I guess she was just a friend of yours, right?" She couldn't be more jealous. You're the perfect girl for Ellie, she's in love with you, and just seeing that you literally were with a friend, alone in the apartment...

It makes Ellie's thoughts quite intrusive.