Can S2 visa be extended?

Hi !
I'm 22 years old and my mother works in china as a teacher and has got a Z type. My mother wants me and my grandmother. my mom' s mother to come . The query is that now it's June and my mother's Z type gets over in August and will be renewed for another 1 year . I know the S2 type issued to me will be till August or till her Current Z type is valid. Is it possible to extend my S2 type in mainland when my mother's Z type gets extended for another 1 year or do I have to exit the country or what will happen in this situation. Many Thanks