#4 Carmella vs. Becky Lynch vs. Asuka vs. Charlotte Flair
Long-suffering Becky fans probably won't like this option, but there's no doubt that a multi-woman match would be the best option for the SmackDown women's championship. Carmella is a terrible wrestler and would only put on another 1-star match in singles competition, stinking Brooklyn up. If Charlotte and Asuka couldn't carry her to a good match, Becky won't be able to do so either.
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A fatal 4 way, on the other hand, would hide Carmella's weaknesses and present us a very good match to compete with Ronda Rousey and Alexa Bliss, as Charlotte, Asuka, and Becky would make some magic out of it.
The biggest danger in such a scenario would be Carmella pinning Becky to retain, but given the unusual circumstances to setting up the championship match at SummerSlam next week, a multi-woman match is the likeliest outcome, since some kind of shenanigans are almost guaranteed, and if not, Carmella would get her win back at SummerSlam. The champion always retains after a challenger beats them for a title shot.