Thanks to the first poster who was very helpful - is it certain she will be told to leave
China? And how long is she likely to be given before she must leave? She works for a
large company here, and I believe pretty much everyone she knows is on the wrong visa
(but again they are all in different cities, met st training). The company has new
teachers flying over for training every two weeks.

Nothing is certain in China. Her 'national' employer must maintain relationships in each province in order to support their ongoing use of illegal foreign teachers. There are not enough legal FTs in China now for their business model. It is conceivable if she is in a poor province in a second or third tier city that the company's 'guangxi' is adequate to protect her. Given the attention that she is receiving however, it is more likely that her employer pushed the envelope by hiring a 19 year old. In the current Xi DaDa climate, local police must ensure a modicum of respectability by periodic enforcement.

The company is replenishing its teacher 'stock' every two weeks exactly because of situations like this. Your friend is most likely going to become inventory 'shrinkage'. Everyone involved knows the 'truth' of her situation and the legal regulations. The relationship between her employers and the police will determine the outcome.