Hey Man,
I live already more than one Year in China - Shenzhen and I have bunch of experience with Chinese gals. First point is - all Chinese girls under 25 - is really unstable about what they say, what they do and what they think- even more if they experiencing sex / relationship with foreigners. You should be really clear with her about what you want. it's because of the cultural difference - here in china is normal to hold hands, kissing each other, go to cinema etc long time - anyway this is already mean like a serious relationship

But as she can speak english and know about ,,foreigners way of dating" she will probably follow you - till the time she understand your meaning - as you see she go for sex quite easy and fast (same as my experience) The problem is after that they become really messy about what next and they mostly waiting your reaction. You should realise what you want from her and show her your meaning about your relationship quite obvious. If you want to be with her you should start to treat her and take care about her like a princess (no excuses if you busy) She will in 99% follow you. If you don't know how to act and you feel messy about her acting - trust me that she thing the same about You :-X She don't know what to think about your acting...That will lead her to takes the things to her hands...
In other case - Chinese Girls can be sweat to many guys in the same time - they ,,fall in love" to everyone who brings them orgasm...as you mention that she say sex with you was amazing - and now you feel from her she loose interest? It's quite weird - is my experience she fuck with someone else (Im just honest) As my experience Chinese girls are really horny if you give them good sex they have no reason to acting like you describe - If she is really into you...
If not - she just acting - it's quite common - Chinese girls can be ,,absolutely Perfect manipulative Bitches"

In the way you never can imagine...Only my advice in this case is - JUST DON'T FALL in LOVE to her too fast

) I know many stories like you describe...Chinese girls are hungry for experience, so give her reason that you are the only experience she want - you will see how she acting. And be more direct with the things you want - if you will see it lead to classic relationship - good for you if you want this. If you will feel weird, or she will just meet you because of sex with you - Im quite sure she have in the same time sex with others and no matter what sweet things she speak to you, or hug you or whatever, she is not into you and just use your penis as she need

) So Be carful mate.
Wish you strong mind!