how many times can i extend my wife's L type visa in Shanghai?

I am a doctorate student studying in shanghai. i have a 4 year RESIDENCE PERMIT. my wife is here with me she is Pakistani.. she has already renewed 2 times her L type 3 months visa for ....how many times can she extend this visa? can she get it as long as I am here in China with residence permit? or there is a limit of extending this visa ?