By the way,

来源: 于 2010-10-28 21:04:26 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

your mother had better not stay in China continuously for more than 6 months. Because she just got the green card, she needs to show that she has the intent to live in US permanently and if she stays in China for > 6 months continuously, the CBP may take a note on her passport.