So headcanon, concerning the cameo at the end?
Lizzie Nichols was a Heather Wells fangirl. She's moved on like everyone else has, but when Heather's dragged through Lizzie's doors (grumping and trailing behind her future sisters-in-law and wedding planner), Lizzie totally had a FREAKOUT and was all "OMG YOU'RE HEATHER WELLS I used to listen to you all the time-"
And Heather's all "Yeah yeah yeah 'Sugar Rush' what happened to me I'm happy can we move on please."
But Lizzie's very sincere about it and she's SO EXCITED because she gets to make HEATHER WELLS'S WEDDING DRESS and the first time she meets Cooper Lizzie tells him he's much hotter than Jordan. (Cooper mentally groans.) And Ava and Tiffany are standing around going "Why the hell are we freaking about this client?" and Lizzie's all "IT'S HEATHER WELLS YOU GUYS."
And the scene at the end, Ava and Tiffany are standing by the door, listening to what's going on while Lizzie's swatting them away to give Heather and her family some privacy god.
(YAY INTER-CABOT CANON CONTINUITY!)