If you will pay her travel cost, you need to complete I-134, and provide your income proof based on I-134 Instructions. Your sister had better bring the proof of the relationship between you and her such as both of your birth certificates.
Read these websites:
http://www.ustraveldocs.com/cn_zh/cn-niv-typeb1b2.asp
http://www.ustraveldocs.com/cn_zh/cn-niv-passporttrack.asp