The U.S. Senate, despite the intent of some of the Framers, is not the House of Lords.    Even the House of Lords is not The House of Lords  It is no longer an  hereditary body.  I have long ago memories of supporting various members of the Kennedy family.  In 1960, as a kid, I campaigned with Myrna Loy for Jack.  Yes, that Myrna Loy.  It was a big deal for me.  In 1965, on returning from the Selma March, a friend and I reported our experiences to Bobby Kennedy's Senate Office.  I think Ted Kennedy's early endorsement of President-elect Obama was magical.  Caroline Kennedy  seems a fine person, but she has not earned the job.

There is a difference between coming from a political family and a sense of familial entitlement.  Nancy Pelosi comes from a political family.  She made her own way in politics.  No doubt she learned much on her father's knee, but it's a long long way from Baltimore to San Francisco.   

There may be a case for appointing someone who will not run when up for election.  They may keep the seat warm, try to complete the work of the person who vacated the seat, or wish to serve to bring up an issue which normal electoral politics ignores.  Ms. Kennedy is only seeking to jump start a political career.  The U.S. Senate is an august and powerful body.  It is not the House of Lords.