While I agree that it's kinda unfortunate for the drama to be over without being resolved, I can totally 100% understand it from a character perspective. Elsa was already willing to look beyond what happened and just wanted to stick with Yvonne from the beginning, Yvonne meanwhile had taken all her strength to push Elsa away in order to protect her, but was left completely and utterly miserable that way. With Elsa coming back to her she's then in such a vulnerable and distraught emotional state that she could not possible resist just going back to status quo, even if she rationally knows that the underlying issue isn't resolved and will cause more pain down the line.
Also really agree with what Koveras wrote a couple of comments above, that's a great analysis of the entire Villainess System problem and how it is basically impossible for Yvonne to resolve. Perhaps doubly so, because she really wants to protect Elsa (and thus herself) from harm, but by pushing her away she causes significant emotional harm too, so she's caught in a sort of paradox until Elsa eventually resolves the situation through her heroine powers