This is my new crack theory: Ava and the WWW were sisters, Ava being the eldest of the two. The WWW was sent to Oz at a young age because of her green skin. The WWW returned to the EF for the marriage of Ava and Leo (note: RENA isn’t retuning. Doesn’t mean YOUNG AVA isn’t coming back). After the wedding, WWW returns to Oz but later learns how Cora killed Ava and set out to “turn Snow White’s heart as black as coal.” She she began to hatch a plan to get back at Cora for killing Ava. But before she could, Regina pushed Cora through the mirror into WL. Thinking that the problem was over, the WWW stayed in Oz. But then she learned about how Regina wanted to make Snow’s life miserable and sought revenge on Regina instead. But then the Curse hit and WWW was stuck in Oz for 28 years. When Emma stayed in SB and time moved again, the WWW didn’t know where Regina had gone. So she has been looking for her this whole time. Now she has come to SB to get revenge on Regina for making Snow’s life miserable because Snow is her niece.
I really like the idea that WWW is Eva’s sister! I’m just wondering why she is cursing Snow & her family too, though.