I've noticed that in Regina's EF page, Ariel is listed as happening BEFORE Skin Deep. It may also be listed like that in other characters' bios...
I think it goes like this:
Skin Deep: Belle goes with Rumple
Lacey: Rumple + Belle hunt down Robin (not Regina related, but I used it to clarify the timeline further)
Skin Deep: Rumbelle forms, Regina breaks it up
The Outsider: Regina captures Belle
Ariel: Regina discovers Ariel is helping Snow
Skin Deep: Regina goes to taunt Rumple about Belle's "death" and asks for help with Ariel
Ariel: Regina poses as Ursula and the rest goes as normal
I think that's how it goes, but if I'm wrong, that's ok too. Thanks for reading.