How does being the President's wife qualify one for the office of Senator?
You or I might naively think that there is no connection: a Senator is supposed to deliberate with the others on the proper nature of legislation to be enacted, and to represent his State's interests as far as is consistent with the good of the Union. Being related to a powerful person has no obvious bearing on this.
But the Powers That Be (PTB) seem to have a different understanding of the nature and role of a Senator. It is not actually necessary to have any connection with the state you represent (Hillary didn't). Nor does it require skills in law or negotiation or modeling outcomes of proposed laws. Reading a teleprompter is the only skill you really need.
Although there is nominally some power associated with the job, it seems as though the PTB regard it as an honorary appointment, offered to a loyal courtier. Since most of the seats are securely in the hands of one party or the other, a party decision suffices to appoint the favored person to office.
Given the character and (lack of) qualifications that some of the "appointees" have shown, I gather that the PTB aren't worried about their pets actually doing any damage; suggesting that the PTB think the centers of power are elsewhere.
Are they right about that? They should be in a position to know, but history is full of self-deluded elites, so I can hope they're wrong. But as devotees of Peter Singer spread I wonder how long before we have a triple-crown winner as senator. It would be a great honor for the jockey, of course. Perhaps honoring each other's flunkies is part of a status game among the backers?