That would be a cameo of Ally from Sunstone (by Stjepan Šejić), for those not familiar with the comic :)

Oh and here's a fun bit: Roomie and Lillian almost made it to Sunstone themselves as cameos! 

(thanks Stjepan for letting me share this, 6 years later ;))

Also, would it have been possible to draw the twins mother even more gnome-ish in that last panel? I'm not sure :D 
Suddenly the anatomy is off and heads grow larger and arms shorter, what can you do?? 

("improve on your art"..? hmm, I'll think about it) ;)

--> This is a rerun of the finished webcomic Go Get a Roomie! You can find these two strips in the old archive >here<!