This fight is closer than expected but it's safe to say Shields won. Marshall took rounds 5, 6, 9, and 10. Marshall should've started early as Shields was taking the early rounds quite easily. Scorecard based on the stats is 96-94 in favor of Shields.
Marshall seems surprised by the resistance, she used to fight low-level fighters when faced with a top-level fighter she cannot react properly, Claressa really knows how to win a fight, bring everything in the early rounds and establish the tempo of the fight, this is what happens when you have not fought a fighter who can offer resistance and this is the first time that Marshall faced tough opposition, Claressa claims that this is her toughest fight, but based on what the boxing world has seen its Marshall facing the toughest fight of her career.
https://www.boxingscene.com/mikaela-mayer-i-genuinely-believe-baumgardner-knows-she-lost--169801
As I have scored it, I favor Baumgardner winning her and I don't think that Mayer was robbed. Of course there are rounds that are very close, but the way I see it, Baumgardner has the edge with her jabs.
I think there is no rematch clause as Baumgardner will fight Hyun-Mi Choi, the WBA champion.
I already forgot but I think Baumgardner hugged Mayer and thanked her after the decision was announced. Mayer responded but her face and mind were still shocked by the result.
https://www.boxingscene.com/baumgardner-i-want-choi-next-what-i-planned-on-what-i-plan--169816
So there is a unification fight in the horizon here, but we will see if Choi is willing to be the next dance partner.