Based on this, I think I may have been a little harsh. You didn't cite specifics in her history, nor did you make specific objection to the argument or facts of the OP. However, you also didn't explicitly say they're wrong; you advised vigilance. As there's nothing wrong with that, I now think I owe you some apology.
That said, I still believe that you came across like a partisan mudslinger. And I stand by my claim that an effort to defeat an argument by addressing its author rather than its argument or facts, is by definition an ad hominem attack.
If you go read the OP, you'll find that it's really an exercise in balance. There's not much factual in it, nor does there need to be. Nor does she really come out on one side of the argument or the other. All she's saying is that the situation isn't as simple as "the government identified a problem and fixed it for us", and I think she makes that point well.
In other words: "this person has been known in the past to misrepresent/misreport things" is perfectly valid to point out, as such a source should be taken with a grain of salt and subjected to scrutiny. Megan McArdle is one such source.