It would be a lot easier for you to come to China and visit her than for her to visit you in USA.  Basically, for a non-married Chinese national to enter USA for a 6 months period, the only visa that applies (short of her pursuing some sort of studies there under a student visa) will be a tourist visa, but those are normally granted for shorter periods of time, and she will have to prove beyond any doubts that she will return, show a bank account in China with more that 1/4 million yuan for over 6 months at least, and own an apartment here, and have a job, etc.

The other possible visa will be a Fiancee visa, but those take an average of 9 to 12 months, a lot of paperwork, time and effort, and will cost you a few thousand dollars.  with that type of visa she will have 90 days from day of entry to either marry you or leave th country, not 180 as you or her desire.

Between lawyers, trips by me to visit in China. documents, etc, I probably blew close to $25,000 US dollars in the whole process of a K-1 visa.

Look mate you have valid question but when you try to execute your plan you will find lots of complications. I am from UK it took me more than 1 year to arrange a visit visa for my Chinese GF, I remember I produced more than 10 types of documentary evidence such as my financial status, my GF financial status, evidence of work from both sides, evidence of relationship from both side, evidence of country ties and much much more, after producing all still  British embassy in Beijing refused my GF visa, then I appealed against the decision and took my case to London in upper tribunal, there it took 8 months for hearing and after a hard struggle of more than one year she reached to UK.  

Basically US visa system is very similar to UK visa system.

I wish you good luck.