I think Regina needs to place blame somewhere and on someone she can actually hurt. Rumple is basically untouchable (she even says you can hide behind your dagger.) And she can’t go after the people Rumple loves because 1) Belle is already in the hospital without her memories and 2) she can’t hurt Bae because he’s Henry’s father.
Old habits die hard and hating Snow and wanting revenge on her is an old habit that Regina finds really really hard to let go.
All of this! And even though I wish Regina could let the Snow-hate go, because it’s been misplaced right from the start, I must admit, I’m looking forward to a bit of Evil Queen on the rampage in SB.