How can Sally be Sallye? :)

I have an acquaintance. This woman has a very common, old-fashioned name, like Mary, Lucy, Sally, Nancy, Patty, etc. However, hers has an "e" on the end of it, following the "y". Her daughter is also named an old-fashioned name which normally ends in y but she has an extra e on the end, too, like Bettye (not her real name). The mother and daughter get TOTALLY bent out of shape if people misspell their names. I say they are the ones misspelling them. Those e's don't belong there to begin with. Can anyone give me a legitimate explanation for the origin of the extra e on a name ending with y? This woman drives people nuts being so picky over this, but we think the spelling looks really lame, and that they are completely wrong to add those e's! Thanks.