If a jointure is made before an intended wife becomes of age, or during her marriage, the widow may, at her election, waive the jointure and demand and have her dower.
If a jointure shall, through any defect, fail to be a legal bar to dower and the widow, availing herself of such defect, shall demand her dower, the estate or interest so conveyed or assured to such widow shall thereupon cease and determine.