From set pictures:
http://vancityfilming.com/once-upon-a-time-regina-and-cora-use-magic/
From the description of The Queen is Dead we know that Cora goes looking for one of Rumple's possessions...looks like she finds it.
We also know that she breaks down the barrier to Gold's store from this:
http://24.media.tumblr.com/8654b506724e81a6a10eb33dd9f3e355/tumblr_mgyevzXfZU1s29wsyo1_1280.jpg
Right now I'm thinking that this may be the episode that Regina finds out that Neal (if Bae) is Baelfire and Henry's father. It's the only thing I think would stop Cora from killing Rumple. If Rumple turned out to be Henry's biological grandfather I think Regina would surmise that helping Cora to kill him would mean Henry might not ever forgive her. I thinking she might stop Cora.