Very strange, especially since there's no Hebrew on stone, no mention of her father's name, and on the other hand details of both the married and the maiden name.
I'm making up a story: Was Mr. Dawson Jewish? If not, was she perhaps disinherited by her parents? Some striclty religious parents even sit Shiva on a descendant who marries outside the faith. Is the stone the brothers' way of stating "she does too belong to our family!"?