You could refer her to http://www.isisonline.org.uk/
I found the information they present on research about children's sleep to be non judgemental but up front about the lack of research into controlled crying but that it does appear to have short term 'improvements' in sleeping but the possible effects (damage) is unknown as no one has studied it. This website doesn't provide a guide to what you should necessarily do but rather information on the evidence of research and allows parents to make their own informed decisions.
The other great resource I've found to inform me of my child's development including sleep to be 'The Science of Parenting'. I don't think there is a quick link on the Internet but that you actually have to get the book and read it, but it can arm parents with scientific information on which to base parenting decisions such as CC or attachment parenting.
IMO if a parent is going to instigate deprivation methods on very young children they need to do it in an informed manner.