A friend of mine will be leaving for China doing missionary work. She is currently purging her closet and is having difficulty deciding on what to donate/keep and bring to China with her. Does anyone have any advice on how to best purge clothes and personal belongings before making such a journey? For example, she has many skirts, but is not sure if she should wear them in China. Also, she is wondering what length of shorts will be appropriate to use when teaching in schools, etc.

do the Chinese actually want her - short or long skirt. Is this 1908?

She should keep some of her clothings. Don't purge everything! Long pants would be appropriate as the weather there can get chilly in the winter months.

She should dress as Christian as possible so that the Chinese know what they're getting into.