Billie. She is an off the rocker type of person. But it will be even more satisfying to hear Jackie calling after him. She'll just shake her head and smirk.

Maybe...
Cole: "Cmon B there has to be a good explanation to this."
"Well, he likes light, and I'm dark. I'm not his type... I mean were friends and..."
"You wish it were more."
"Well... yeah. I mean no. I mean... shut up." She'll just see Cole smirking and sigh. "I've always wanted it to be more, Cole."

It's actually quite traumatic for Billie. You'll actually get to see her afraid. But the  again when a secret like hers, I think I would be too.
And she's still really getting to know Clary at this point. Enough to trust her, but not enough to consider her her best friend.
"Please." Sassy Clary is laughing and trying to be Sassy too.