I'd go with a bottle of Chanel fragrance (maybe Eau Tendre or Coco) or some other well known luxury brand and get the shopping bag with it (Women love those bags). It can be purchased in China or HK but it's more that 50% less in the states. Almost every time I come, my girlfriend has me bringing 30ml bottles of Chanel to give to her friends and family.
In general, many of the "luxury" brands can be had in the States for much cheaper. @
moondog suggested a Micheal Kors bag, that's a great suggestion or something like a cheaper Coach bag in that range. Any of the mid-level designer bags that can be had in the $150 price range would cost a lot more over there. Cosmetics are also a big hit from brands like Guerlain, YSL, Dior, Lancome, etc. Possibly shoes or jeans but getting the fit right could be troublesome. I'm very frequently bringing basketball shoes for my girlfriend's sons and nephews, Nike, Adidas, etc.
Chinese people love those Ferroro Rocher candies, although plentiful in China they are always appreciated. If you're based near SFO, that's California wine country so a lot to choose from there. Maybe some Sourdough bread from San Fransisco. If you're a coffee drinker, bring some good coffee and a cafetiere and show her what that is all about.