The *recommendation* is not to use it until 6mths old at least - not at all would be preferable, but if you feel it is the only option you have available to you there is a difference between controlled crying and then cry-it-out or extinction crying - basically where you just leave the baby to cry/scream until they stop/fall asleep etc (which can be HOURS) - controlled crying is a little more measured - you put them to bed, walk out, if they cry you go back in after 5 minutes, resettle with no eye contact and then walk out and keep doing it till they fall asleep. It is quite labour intensive really.

Bare in mind though that it may not work at all and your DD may still wake through the night - which is normal for them to do up until toddlerhood. If you choose CC then you will have to do it each time she wakes. It isn't a magic cure-all for sleep.