Middle English obsolete form of her.
Examples from the Web for hir
But the empresse and hir brother would not hearken to any agréement, except that the realme Geruasius Dorober.Chronicles of England, Scotland and Ireland (2 of 6): England (4 of 12)|Raphael Holinshed
Mr. Rawlegh his letter unto me of hir Majesties good disposition unto me.The Private Diary of Dr. John Dee|John Dee
But the maid by hir praiers pacified Gods wrath towards him, so that his sight was againe restored to him.Holinshed Chronicles, Volume I, Complete|Raphaell Holinshed
Which the Gentlewoman assured hym to doe withoute fayle, and taking hir leaue of him, she retired home to hir house.The Palace of Pleasure|William Painter
As this wes said, Ledingtoun smyleit, and spak secreitlie to the Queue in hir eare; what it wes, the tabill hard nocht.The Works of John Knox, Volume 2 (of 6)|John Knox