Style guide

As a general rule: -y is an English suffix, whose function is to create an adjective (usually from a noun, eg creamy); -ie was originally a Scottish suffix, whose function is to add the meaning of "diminutive" (usually from a noun, eg beastie).

So in most cases, where there is dispute over whether a noun takes a -y or an -ie ending, the correct answer is -ie: she's a girly girl, but she's no helpless girlie. Think also scrunchie, beanie, nightie, meanie ... There are exceptions (a hippy, an indie band), but where specific examples are not given, use -ie for nouns and -y for adjectives