Re: If you were going to buy a small stash...
I will just say, if her baby is frequent pooper... 3 wont be enough. We have three flips and always end up in a different system by the end of the day because my son poops a lot. 18 prefolds is probably fine, though I might would go for flats since flips are made for trifolding.
Mom to Isaac born 5-24-11 and Leah 2-19-13