Because it looks like it could be happening:
Stephanie McMahon Says She's Training For WWE's WrestleMania 32 - WrestlingInc.com
Wonder who her opponent could possibly be. Charlotte is a heel, Paige is a quasi-heel, Becky is the top babyface but I don't see her working a program with Steph, Sasha Banks is injured and I doubt they'd break her free from Team Bad and push her hard in a program against Mrs. HHH this fast even if she wasn't.
I think it's almost safe to say Ronda Rousey is still out. She has other commitments (Roadhouse remake, etc.) and I think the devastating KO loss she suffered to Holly Holm may have put a damper on their plans anyway, since she no longer has the same aura surrounding her unless she can come back and defeat Holm and redeem herself.
I have no problem seeing Stephanie perform. She's the best heel on the show other than Vince himself, and she outperformed 99.9% of the Divas when she wrestled Brie Bella at the '14 Summerslam.