I believe that Samuel and Susannah lived in Tippah - and they are both buried at Mt. Pleasant near Blue Mountain - not too far from Jacob's Chapel Methodist Church (if you know that area). Other Beaty-related family members are buried there as well. However, I believe there is probably a connection between the Union County and the Tippah County BEATYS - at least between those that share the same spelling. There were BEATTYS in both counties too, I think, but I don't know of a connection between them.
I don't have enough information about the Porters in either of those counties. Certainly some of Susannah's family could have migrated to Mississippi around the same time she did.
Are you related to the Porter family in either of those two counties? I suspect Alexander Porter who moved from SC to Ohio is Susannah's uncle, but I have no proof. I'm still trying to pin down for sure where in SC Samuel and Susannah were living prior to moving to Tippah County. I believe Susannah's father was also named Samuel.