Or, the straight-line version:

They own the property together per the life estate. He, the business tenant, pays to the estate for occupancy and shoulders property maintenance costs. She gets the income from the estate, but cannot touch the principal. He wears two hats. And his right to the property should be protected within the life estate, and she cannot make him lose that, if he were to need to rent a different place for the business, because personally (one of his hats) he is the joint owner.

But people can threaten to do all sorts of things to each other, of course.