(Not-Senator) Vicki Kennedy

In an interview on Oprah, Ted Kennedy's widow, Vicki, explicitly disclaimed any interested in running for her husband's Senate seat.  Instead, after a quick reshuffling of Massachusetts law on the subject, Governor Deval Patrick appointed former DNC chair Paul Kirk to fill the post until a special election could be held.

It's interesting to note (albeit mainly for history geeks like myself :)  ) that there was a time when Mrs. Kennedy, as the widow of the sitting senator, would've been the first choice to be an interim appointee.  The second woman to sit in the US Senate was Hattie Caraway, who was originally just to be an interim appointment to fill the seat of her late husband, pursuant to tradition in the state she was from.  She surprised everyone by running for the office in her own right the following year (1932).  She not only won that but was also reelected in 1938.

Many subsequent female Senators also got in via the widow's walk.  The widows of Huey Long (1936), Harlan Bushfield (1948), Hubert Humphrey (1978) and James Allen (1978) all got in that way while Jean Carnahan was appointed (2001) to fill the seat of her husband who had died just before the election, to late to be removed from the ballot (you may remember the enjoyable incident of John Ashcroft losing the election to a dead man).  Many of the women who were appointed were generally short-term, even if they weren't the widows of sitting Senators.

Margaret Chase Smith was elected to the Senate in her own right but had started in the House of Representatives by succeeding her deceased husband.  Likewise, 1992 became known as the "Year of the Woman" because of the surge in the number of woman Senators (to a whopping six!) that was occasioned by the response to the Clarence Thomas confirmation hearings.  One might hope that the idea of women as being genuine electoral threats in their own right (beyond the periodic isolated case) has put paid to the idea of a widow as being a placeholder.