I can see why. There is a personal aspect to it. She has been smeared by NR in the past, both as an alleged bigot and as a supposed Bircher - including by Buckley on the specific subject of McCarthy. And she was and is simply right on the subject, and those were all smears. Going right back to the rift between Ike and McCarthy in the 50s really.
In the circumstances, I think a twist on the knife is just what is needed to wake a few people up.
If, as you say, NR gave the review assignment to Radosh in ignorance, then indeed they need to correct their mistake, and not just leave it to Ann to do so. Otherwise it makes them look guilty too.
Strange thing is that Stan Evans is one of the original editors of National Review. Also, Bill Buckley's second book was McCarthy and His Enemies, co-written by his brother-in-law, Brent Bozell, Jr. It was written during the original McCarthy controversy from a generally pro-McCarthy viewpoint.