#3 Becky Lynch's character change

One of the biggest surprises of SummerSlam 2018 and perhaps one that will be looked back as a huge change in women's wrestling was Becky Lynch's heel turn following her match against Charlotte Flair and Carmella.
Lynch faced Flair and Carmella for the SmackDown Women's title which was then held by Carmella. Charlotte won the match after hitting Becky with the Natural Selection and winning the title. Following the match, The Man attacked Charlotte, confirming her heel turn, and she explained her actions on the following week's SmackDown Live show.
Despite being a heel, Becky got the fans to cheer for her which eventually led to a feud with Charlotte and a subsequent face turn, as well as the beginning of The Man gimmick, which was one of the highlights of 2018 as well as 2019.
One year on, Lynch is the RAW Women's Champion, the title she won at WrestleMania 35 when she defeated Ronda Rousey and Charlotte Flair.