My main sources for Margaret Sedgewick are ancestry.com. I pay yearly dues to subscribe, so I don't know how much access one would have if not a member. There is usually a lot of conflicting information there. So it is a matter of using your best judgment as to what you choose. I suspect Margaret Stitts and Margaret Sedg(e)wick are one and the same person. Anyway, after looking at a Zouche family tree, I no longer think it was (an apparently non-existent contemporary) Margaret Zouche. You can also see Margaret Sedgewick on the Family Search website. But I saw only two enties, and they don't show whom she married.
I am always open to be corrected, and would like nothing better than to know for sure who Alice Powell's mother was. Although I don't have a paper trail going back to Alice Powell, I traced a (rare) U5 HVR1+HVR2 match to me back to her. And my grandmother said that her line traced back to Jamestown.