Lots of good answers to the clothing part, but I would like to add some additional stuff about the 'wailing until someone does it' part.
18 months, for both my kids, were the start of their independence and really attempting to communicate. She has discovered a desire or need (to take her clothes off) and a way to communicate it (wailing).
It may only marginally be about taking the clothes off, and more about being understood.
We have been somewhat successful in using 'the fast food rule' from Happiest Toddler on the Block, where you repeat their statement/need first (like in a fast food place), and then go on:
Sweetie, I know you want to take all your clothes off, but you have to wear them since we have guests.
Or whatever explanation you may want to use. Sometimes it works, and sometimes it doesn't, but at 18 months she is right at the age where she just want to be understood.