As a scientist, you use anecdotal evidence. Oh dear.

Wow! Madness! Even if there were any evidence to suggest that allowing a bitch to have a litter has a calming effect on her, the end does not justify the means! In this massively over dog populated world it is a ridiculous thing to be suggesting! S if any of her litter also turn out to be of an anxious nature do you recommend breeding from them too to solve the issue?!

How about just accepting that that dog has issues, neutering it or using some other method to ensure it doesn't produce a litter and making the best life you can for her!

Someone who recommends this really doesn't deserve to be working as a behaviourist! It's unethical!