Liv just returned from injury at the Rumble and was runner-up. She was also part of the EC. That's really the only noteworthy things she has done since, other than be part of the Rhea injury. Nia was taking everyone out after her return, even winning a match against Becky, which Becky got back of course leading into Mania. Nia was definitely the most legit contender next to Becky. This is why they had Becky, Nia, and Liv as the final three.
One good thing out of this Becky win is seeing the Liv Stans meltdown on Twitter.