Throw her out the window.  Her place is outside.  

In my classes, I do this type of thing regularly.  And the students are only too aware.  

Some of them even bait me deliberately in order to be thrown out the window.  

Even though I can usually recognise this tactic, I throw them out the window anyway. Credit where credit's due, I reckon.

That's how most Chinese are, obnoxious. From the ones making loud noises when you try to take a nap at official nap time (1 to 2pm, many companies seriously have 午休 on the timetable), to the ones being completely disrespectful of your work, there is no hope with such people, if talking didn't work you must go to the next level, kick her out of your class, literally.

Really comes down to how much control you have over what you do.  You can bring up the lack of professionalism.  The professional thing to do is talk to them one on one, however if this doesn't work you can tell them what you will do if they wish to continue their current behaviour in class (i.e., ask them to leave the class).  You could try bringing it up with your superiors to see if you can get their support.  You can try to emphasizing teamwork and how it will be beneficial versus focusing on the negative traits you don't like.  Like more of what you want versus what you don't want, and use language like we versus you (e.g., we can do...vs you can do).  

I had a similar experience in the US working in a youth fitness program where a volunteer (around 16 or 17 yrs old)  came in dressing like the next D (gangsta/Home slice/DJ Fresh).  And I told him it was unprofessional and he needs to change (we provide the shirt part of the uniform for free).  He made some rebuttals but I was like this what we do and he changed and pulled his pants up.  I didn't think it was right that kids had to stare at his underwear, plus I emphasized that we are role models for the kids.  I started with the positive part and after the rebuttals I went to this what I need you to do if you are going to volunteer here. 

Good luck with whatever you do.

I am not a teacher but you call her your assistant. Do I get it right that you are not able to handle a relatively small issue with your subordinate?
Well, then good luck to you and "nature" bless your students ...
But let me be constructive. Did you try to talk to her and address your point? Looks like you did. So did you try to take disciplinary measures against her (if needed even publicly in front of the class)?
If this all did not work and you have no authority to restrict her from attending your classes so did you address that to the school headmaster?
If you did all of the above and the result is that the school is more concerned about your assistant than you than you are confronted with.serious situation.
But may be it's just a small issue ... It should be easy for mature person to handle one presumably "immature" one. And if it's not so ...

i had an assistant who got a bit oversensitive and hostile, and decided that she didn't have to translate anything i said in class anymore. all because of a silly rule "no Chinese in class" that the boss dictated to make his school stand out from the competition. of course everyone spoke Chinese in class, except her when i needed assistance. she intended it as a personal act, but i didn't take it personal. i still get my paycheck even if the quality of the lessons are below par. i didn't even report the problem, because she had the rules on her side. oh, and she was head of the teaching department at the time. i had gone through the discussion before: "you should control the class (of ill-mannered xenophobes who don't respect you in a foreign language) by yourself."
she left for a job in a different city, and although she claims she's happier and it's more professional there (facesaving makes it difficult to believe what anyone says), she visits the school often.
the new department head is male, and is more respectful when telling me what to do. they're still ordinances dictated from above, but it helps when people don't take disagreement personal.

i always interrupt a class and say someone is talking instead of listening, and ask the talker to share their story with the whole class, they usually dont say anything in response, so i make suggestions about the conversation

so you were discussing how ugly i am

so you were discussing how handsome i am

so you boyfriend got you pregnant and you need a loan for an abortion

so your father has a mistress

so you mother slept with your bf

so your degree is fake and the school gonna fire you

no,no,no,no, well i keep making suggestions until i get it right or you want interrupt my class anymore, which option would you like bitch.

not very professional but it always works. my favorite response was teaching assistant that said nobody likes you, and i said if want to be liked i will buy a puppy and when it hates me, i will eat the damn thing and buy another one, the look on her face was priceless.

Personally, it's either her or me... If she's doing this consistently even after it's been brought to her attention, then I'd be telling the supervisors that you won't be teaching in that room while she's there. Simple as that. Of course, you will have to go through on this, and also to stick to your guns. NO matter what the supervisors say, you still don't go into that room while she's there.

You'll usually find that we FTs have more power than any local... cos there's far fewer of us than them - we're harder to replace.

Last year I worked in Primary school in small city in Xinjiang. Mentally challenged kids must be in the classroom till Grade 4, mixed with all other kids.

As I started to work there, I wasn't aware of that, 'cause we have special schools for mentally challenged kids in the West.

On one occasion in one of the Grade 3 classes, some 10cm long metal screw suddenly flew through the air, and landed on the other side of the classroom.
Kid dismantled screw out of his metal chair, and.....Every chair in the classroom had 2 screws.
I didn't have any other choice, but to make friends with the baby, in order to have class with other kids.
He was standing or walking with me through the class during the reading lessons, and on one occasion Principal stepped into the classroom, and saw us both 'teaching' together. Following week, I had Chinese teacher in all classes with mentally challenged kids.

When we met with 'metal screw kid' outside at the lunch break, he would always reach into my coat's pocket, and grabbed candy ready for him. I was even teaching him how to share.
He was my buddy.

Tell the school that if she is still working there, you will leave. And leave.

1. Did you confront the bitch outside of class and give her an ultimatum that if it happens again you're going to come down on her with the wrath of 10,000 Wangs? 

2. If yes to 1 and she didn't listen, make your concerns clear to management. If you're a decent foreign teacher, you are way more valuable to the school than a Chinese TA. If she doesn't shape up, she will be fired unless she got the job through guanxi. At worst, the school can probably have her work with a different FT.