My wife and I will transit in Beijing and visit friends. Our layover is 9 hours.

I read the requirements for US citizen and understand. My question is: My wife is a Thai citizen (with Thai passport) and also has a green card from USA. What steps must she take to obtain a visa that will allow entry in to Beijing for our short layover. FYI our flight details: LAX>BKK & BKK to LAX via Beijing.