Dorothy Kilgallen did not kill herself so much as drink and drug herself to death, and it was never claimed she committed suicide. Her death was determined to have been caused by a combination of alcohol and barbiturates. Regarding whether it was a suicide or accidental death, New York City medical examiner James Luke's report stated, “acute ethanol and barbiturate intoxication, circumstances undetermined”.

Her supposed "bombshell" private interview with Jack Ruby was a brief conversation during a recess at Ruby's trial, in full view of dozens of people. She had also already leaked Ruby's testimony to the Warren Commission well before her death, and, quoting Newsweek,

It was just another in a long series of leaks. Although the commission has tried to maintain a screen of secrecy, it has been as effective as a sieve. While the leakage has been kept to a minimum in Washington, newsmen in Dallas and other cities have easily breached commission security. Not only have some of the 543 witnesses and their attorneys been "cooperative," but the commission, as a matter of legal etiquette, has provided them with verbatim transcripts of their testimony. In such an atmosphere, it is surprising that the Ruby testimony wasn't published in full before now.
Certainly, the 102-page document, at least the Kilgallen version, contained a great many fascinating insights into Ruby's deteriorating state of mind, his attorneys' inability to restrain their erratic client, and Chief Justice Warren's infinite and understanding patience.

"They" ruined her reputation? If by that you mean a bunch of conspiracy theorists who let her death overshadow the rest of her life, then yes, "they" did. But she's hardly the only victim.

As to Ruby himself, he personally stated that he was in the neighborhood that morning because dancer Karen Carlin had made a plea for him to wire her some rent money; the Western Union was near the jail. He was attracted to the bustle at the jail when he finished his business there. Had he not initially made an illegal turn to get a parking space, he would have missed the 30-second window when Oswald was being escorted for transfer. And Oswald himself must have conspired in his own death, if there were such a conspiracy, because he would have been gone already had he not requested they turn back to get his sweater. There was no way to foresee or plan any of these events, just as Oswald got a job at the Book Depository weeks before Kennedy's visit to Dallas and his motorcade route were even decided. He was not put in place to be the assassin: he chose to shoot Kennedy once he realized he had the opportunity.

Both Oswald and Ruby were little men who wanted to be something bigger. That's all.

A mob-connected nightclub owner, Ruby, assassinating the assassin, was always fishy.

Ruby said he had been distraught over Kennedy's death and that his motive for killing Oswald was "saving Mrs. Kennedy the discomfiture of coming back to trial".

G. Robert Blakey, chief counsel for the House Select Committee on Assassinations from 1977 to 1979, said: "The most plausible explanation for the murder of Oswald by Jack Ruby was that Ruby had stalked him on behalf of organized crime, trying to reach him on at least three occasions in the forty-eight hours before he silenced him forever."

Ruby repeatedly asked to speak to the members of the Warren Commission. Ruby asked Warren several times to take him to Washington D.C., saying "my life is in danger here" and that he wanted an opportunity to make additional statements. He added: "I want to tell the truth, and I can't tell it here."
[Wikipedia]

If he were going to do a hit for the mob, presumably he'd be prepared to get caught, go to jail, and keep his mouth shut (which he did - until the mis-trial, at least). If he were doing it out of personal distress (for the First Lady), presumably he'd not be so inclined to get caught. He shot Oswald in a police station basement!

We may never know the truth. Meanwhile, the stories still sell.

Recommending a book: FAMILY SECRETS by Russ Baker. Bloomsbury Press

Probably not. Conspiracy theories are for assholes. The guy at HowThingsWork is a prime example.

Maybe some of those answers are in the files that are still hidden after the last administration chose to keep them sealed. Must be some pretty interesting stuff, and only a few people know what's in them. A secret only known to a few powerful people can be a dangerous thing.

Dorothy's big mistake was in telling people what she was going to do and her JFK info was going to center on Carlos Marcello, New Orleans, Oswald, and Ruby. Pills and alcohol do not mix and she may have taken some. People did that a lot back then. That does not explain her missing files and notes and other things that do not match up when you look at her death.

Possibly

Wasn't Dorothy Kilgallen a panelist on "What's My Line"?

No. She probably died of an accidental overdose of alcohol and barbiturates. If anybody offed her it was the mob. She wrote some secret stuff about the mafia and how Frank Sinatra was associated with the Genovese family. I still think not.