Middle-earth Mysteries

[Balin999]

Sam says his cousin saw a tree on the northern borders of the Shire walking "Seven feet to a stride if it was an inch".

You're forgetting that the Entwives didn't resemble the Ents in form and statue.
Treebeard says that they had round faces, were smaller and more concerned with the Earth and blossoms. So the tree in the Shire could only have been a male Ent.
I hate to say it, but I'm rather pessimistic concerning the entwives.
Since they had their gardens in what later became the Brown Lands, they might have died in the Great War.