I can assure you it is entirely in vain. Here's pretty much why:

"Face" is the most important thing in China. If she admits her faults, in her warped mind she is losing face. Therefore, she is entirely perfect as she is because she can never admit fault or mistakes for fear of losing this face. She has convinced herself that she has no fault and is a perfect "human being" and needs absolutely no advice from a bunch of dumb lao wai that are just trying to "ruin her face and business" when in fact it is her unwillingness to co-operate with her most valuable resource (foreign teachers) that will ultimately cause the destruction of her business and reputation.

Afterward, she will tell everyone she knows how evil foreigners are for screwing up her business.

And that's why the whole face thing is utter crap and why she will most likely never take our advice.

I got a better chance of having a meaningful conversation with a brick wall.