Graduate visa vs extending student visa.

My daughter's student visa is expiring end of March and after completing a diploma she has two options. Applying for another student visa, or applying for a graduate visa. At the moment applying for another student visa is getting very difficult the few universities that do enrol international students on first semester are about to close applications. Due to a delay in getting the diploma and transcripts hence the situation. If an application for the visa is lodged now, will she be able to start classes before the visa is granted? And what processing times are we set to face waiting?
Option 2 is applying for a graduate visa. How long is the processing and what can she do and not do while awaiting the decision??