Regardless of if she goes on last she is undeniably about to bring in the most viewers, especially casual fans. We know WWE is obsessed with "making history" with the women and main eventing Mania is the last big thing at this point.

Say what you want about her overshadowing or burying the division but Rousey is 1000x bigger than the entire division and if she's signed full time you make her the center of the division ASAP. The rest of the women can be happy counting their money they'll make on on the back of her.