Nope Zach likely came in the year after Billie came to the school. 

[S]Really though I can see Zach being a little scared of Clary when she gets hyper.[/s]

I made a couple outfits for Jo.

Zach was just standing there listening to the girls talking. And he'll smile at Dahlia when she looks at him. Seeing Billie wink at him. " Yeah, I can totally show you around. Where would you like to see first?"