Shouldn't: Stacy Kiebler

I was originally going to put Kelly Kelly here, but she was announced for the event within the last few days. In essence, both are attractive blondes who were in WWE because they were attractive and not because they can wrestle.
If you want to be in WWE and not wrestle, you better be a great talker (neither were) or a fantastic interviewer/broadcaster like Renee Young or Charly Caruso.
Is this man the funniest man in wrestling?
The main difference between Kelly Kelly and Stacy Keibler is that they decided to give K2 a title reign. Both used WWE as a platform to become famous and further their fame.
Unlike Kelly Kelly, however, Keibler has stated that she was embarrassed about her tenure in wrestling and feels it is beneath her. She also has reportedly ignored fans and looks down on them. She would only come back for a big-money offer.
For those reasons alone, she shouldn't be welcomed back. She was never a skilled wrestler and was mainly hired in WCW and WWE because she had long legs.
If someone is embarrassed by your industry, chances are you shouldn't reward them with an appearance. It would be better served going to someone who actually respects the business.