I am wanting to buy my mother a bucket/crusher hat (i think that's the correct name). Anyway, I was wondering how they fit. I don't know whether to go with the p/s or the m/l. I made up an excuse for her to measure her head, which is about 21-22 inches. I hate having to exchange items since the Coach store is about 45min-1hr away, so I want to get the size right. Any help is appreciated!!!