Why? So she can stop having matches with men (most of what has got her over), and probably lose to Becky Lynch for no reason? Or be partnered up with Alicia Fox or some shit? Tessa is doing good things outside of WWE. I'm sure she has no interest in abandoning that so she can be told exactly what WWE wants her to say and do.
With 100% honesty, Tessa is almost at the point where she could win a heavyweight title and it would be believable. Throwing that away to be another woman on WWE hardly seems like a great idea to me.
What do you mean lose to Becky Lynch for no reason? if those two worked together the creative team would put together a reason for her to win or lose with some kind of storyline. WWE has done intergender matches not too long ago so its not impossible to think that they'd try something with Tessa if the opportunity presents itself to them.