"a witches curse" okay hear me out here, I am probably incorrect here because I haven't re-read, or even thought about this series in a while, but could the curse be somewhat of a villainous system? I heavily doubt it but there's not really anything in my brain right now that can state what the curse could be, which will probably be explained in the next chapter. Real quick tangent on the villainous system I mean ever since Elsa and Yvonne kissed, "breaking" the chains of the villainous system, the story hasn't really brought the villainous system up, however now that Yvonne has gone back in time the breaking of that villainous chain no longer works as the bond has no longer broken (unless if the villainous system breaking is one of the things brought over from the parallel previous world to the "time travel where Yvonne and Elsa are young world"). So I wonder if the villainous system will ever be brought up again like if they bring it up with the "curse" Yvonne's mother has, or if Yvonne gets her villainous system back, or they will bring it up both times for Yvonne's mother and Yvonne herself, or they will only lightly bring it up for the rest of the story. I'm more thinking of the last option, and I am most certainly going into conspiracy hell-hole territory, so I'll just stop talking here.
Edit: I just realized how much I talk about the villainous system I think i need to gain a hobby that isn't constantly thinking of the villainous system