I kept poking around on Mary Jane Helm Tompkins and look what I dug up from a medical journal of 1857:
Preservation of a Body. — The Vicksburg Sentinel, of Mississippi, relates the following: "On the 27th of February the remains of Mrs. Mary Jane Tompkins, first consort of Hon. P. W. Tompkins, former member of Congress for this district, and a sister of ex-Governor Helm of Kentucky, were disinterred. She had been interred seventeen years on the 4th inst., enclosed in a zinc coffin, which was filled with alcohol, which was re-enclosed in a wooden coffin, and all carefully packed in charcoal. The wooden coffin and top of the zinc one were somewhat decayed, but the corpse itself was in a perfect state of preservation, features natural and hair as flexible as in life."
So the "Mrs. Tompkins" who didn't like Mary Todd Lincoln was P.W.'s second consort. And my assumption on who Mary Jane Helm married was correct.