My girlfriend (Russian citizen) lives in China under a business visa. I (American citizen) would like to go visit her for a few weeks, and it seems that the S2 visa is the appropriate one for me to get (if I should still get the tourist L visa instead, please let me know!). However, I have only seen references to people "working" or "studying" in China as being able to write the needed invitation letter for the S2. Does a business visa count as "working", and, if it does, can she write me the needed invitation letter?
The S2 is issued to family members of work Z and student X visa holders. The S2 is not issued to family members of business F/M visas. You should apply for a tourist L visa.
To be clear, business F/M visas are issued for people working in China but normally employed by a foreign firm and invited by a Chinese company to conduct business between the foreign and Chinese firm. The work Z visa is issued to people working in China for a Chinese company with an invitation from a government agency.
In any case, I have a Z visa but my brothers and parents visit me on L visas, as do every other foreign persons family I know. A tourist L visa is quite acceptable for short stays.