If you watched the Royal Rumble and Monday Night Raw then it comes across as if the plan for WrestleMania is for a singles match between Ronda Rousey and Becky Lynch for the Raw Women's Championship.
The feud between Lynch and Flair continued on SmackDown Live and that will lead to at least one singles match on pay-per-view before Mania because Lynch vs. Flair is listed on advertisements for the Fastlane pay-per-view in March. It's possible that they will also wrestle each other at the Elimination Chamber pay-per-view.
Flair vs. Rousey was the original plan as of a year ago but Lynch caught fire towards the end of 2018 and the decision was made that she would be in the mix as part of the Mania main event. Card subject to change but we are told that the current plan is for the Raw Women's Championship match to close out this year's WrestleMania and WWE will have the winner appear on daytime television to capitalize on the buzz surrounding women headline the company's biggest event.