Dianna Coleman was born in Halifax, Virginia, married John Williams, and died in 1813. Vol. 8, William and Mary College Quarterly Historical Magazine, states that her will was signed by her brother Henry E. Coleman (but I find no other record of him). Her husband was of the executors of Henry Thompson's will. If she is indeed the daughter of Thomas Coleman and Elizabeth Brown, then Henry Thompson would be her brother in law.
I have not found definitive evidence of this fact. The book, The Colemans of Mobjack Bay, show quite a bit of information on the other siblings of Rachel (Coleman) Thomson though not all of them have been listed in wikitree.com as of yet, but not much on Dianna and offer no information on Henry E. Coleman (her brother?)