Why would she suddenly go there on her own
I really don't think Zeus will play any role with getting Big Mom to Elbaf, could be many reasons I don't think her suddenly wanting/tracking Zeus back and going to Elbaf.
Could be now lets say she does have Germa tech that she starts a War of Attrition of with Giants now able to breach her way through to Elbaf and hell just enslaves/forces Elbaf to join her or wants to conquer her homeland, especially since she can no longer make her own giants (since no matter what Its been one consistant thing in the series, no ones been able too)
Could be she learns that the last road poneglyph is on the island.
Some deal and alternative stuff within Loki considering we still need to know more about that bit in there history cause if the marriage did go through Elbaf would be hers.
Or just how Luffy and Law alliance was leaked (Kidds too), similar plans could be leaked out to the world thats spurs it, or even major event like Kaido going down or what happens at the Revivre cause the major players still left to make big moves again like with Whitebeards death.
I really don't think Zeus will have much ploy in meeting Big Mom again, especially since she could just make another thundercloud homie if she really wants to and Zeus isn't really important/built to be a huge part Big Mom Pirates structure or future.
Now if it where Pudding, that would make more sense considering without her Big Mom goals are up in smokes.
Not only that can Big Mom really track Zeus?
Especially in such a long range where she would know oh there on Elbaf right now lets go.
I just think there are other ways that are more dynamic to get Big Mom to Elbaf then just because of Zeus.
Especially since we still don't have a good emotional/logic reason for Luffy to head there yet.