She's buried under a mound at Meigle in Perthshire is old Jennifer. Guenevere (or Old Jennifer as we call her up here) was a Pictish Queen. They used matriarchal lines of lineage. She collected severed heads as we all know, which was a sort of Pictish hobby. Her fave boy old Lancelot/ l'angelus (all these tales were translated from Norman French and lancelot came from l'angelus - gaelic Aeongus - Angus) was also from that area north east of Perth now known as Angus.
If your looking for a certain last battle site you should check out the traditional battle site just outside Stirling. The River Allan runs into the Forth there. There was a hospital near their confluence there from the earliest christian times. Its name predates the earliest of Arthurian tales. There are still stones which marked that battle at Bridge of Allan and Stirling University grounds.

This Oswestry is just some Welsh hillfort that should be protected. Dont need to dig up Jennifer and drag her sorry bones South. The old skull collector is fine where she is.