I'd be curious of the serious long term issues that she found. I did a bunch of research on this as well and never found any credible source for or against CIO, really. There's a huge spectrum between the different methods too, and I found lots of people conflating "ignoring all the needs of your child" with CIO which isn't really what any of the methods proscribe.

I don't really have a horse in the race, my daughter sleeps wonderfully and has since she was 4 months old or so, but there is a lot of fear mongering on the internet about parenting styles and techniques and the amount of actual evidence is sparser than I'd like. New parents are already neurotic and the internet in general jumps to warning about serious long term issues for almost anything.