Who would've thought that, in this age and time, I'd still be wondering which title to use? At the Catholic-friendly web site linked below, I still am. You see, in real life, the only feudal title that survived in the United States was "Mrs." It may have sneaked in because most if not all English-speaking colonists were still using "Mistress"; "Miss," "Mrs.," and "Ms." are all short forms of "Mistress." Anyway, two different rules evolved during the nineteenth century:
(1) In the North, where the textbooks later accepted as official were published, "Miss" was used with a woman's own name, "Mrs." with her husband's name. When Miss Jane Doe married Mr. John Roe, she acquired the right to sign documents with "Mrs. John Roe" instead of "Jane Doe." Later, "Mrs. Jane Roe" began to be used to indicate that Jane and John were divorced, which Emily Post considered an abomination...but in the twentieth century, less educated people started a fad for automatically calling Jane "Mrs. Jane Roe," possibly because...
(2) In the South, the short form of "Mistress" that was originally written "Mis'" was always pronounced phonetically--like "Miss" before names that began with K, P, S, or T, and like "Ms." before names that began with B, D, or G, and before other names it helped pinpoint which part of the South a person came from. I don't know to what extent this was ever formally "mapped." Anyway, people continued to pronounce the courtesy title for women the same way even if they wrote "Miss" and "Mrs.," and since it was, properly, "Miss Lillian" (or "Miss Rosalynn") for "Mrs. James Carter," there was lots of room for confusion and etiquette and we-are-more-traditional-than-you.
So which title does Priscilla King get? Technically, the Priscilla King who writes this web site is a brand name not a human name. Brand names have neither age nor gender nor courtesy titles. Properly, it would be "Miss Priscilla," widow of "Mr." whatever-my-husband's-screen-name-was-if-he'd-ever-had-one-which-he-didn't. (E-mail existed during my husband's lifetime, but we didn't use it.) In the nineteenth century efforts were made to add "Widow" to the list of titles, and to prescribe that, if John Roe died while still married to Jane Doe, Jane could sign estate documents as "Mrs. Doe Roe"; neither of those ideas caught on.
This kind of mix-up was why "Ms." was invented, and why, when web sites insist on using a title with my screen name, I use "Ms."