Student to Partner Visa

Hey guys, it's been a while since I've posted so quickly a bit of background:

I've been partnered with my wife for too many years. I asked many questions here and got a lot of good help. I personally (ie without agent) applied for several tourist visas and subsequently a marriage visa. My loving wife has now been permanent for some time (ie, we met and she first came to Australia almost 10 years ago).

Since then, we've brought other family members out here on a tourist visa: first her cousins, then her mother. Since then, two cousins have come here on student visas. 

I have done everything myself, except for the student visas. 

Today's question:

- one of the cousins has met with a local Australian and they've been together now for a few months. 

- she's on a student visa.

- she's been in Australia for several years and renewed the student visa in that time

- her current visa still has several months left to run (ie, doesn't run out until early next year)

- whilst she has been in Australia she has lived with me and my wife

- she has since moved in with this new fella

- she has had no other serious relationships in that time (she has dated obviously, but in all seriousness, she hasn't really had the time)

- they intend to marry

- Her student visa expires in 4 months

If she applies for a proposed marriage visa at this time, what happens when her student visa expires?

a) can she keep studying or does she have to stop?

b) can she get a bridging visa to cover the time period from expiration of student visa to decision?

c) should she apply for a new student visa and subsequently apply for a proposed marriage visa?

d) should she apply for a new student visa and subsequently apply for a partner visa once they're married?

How would one decision affect the other?

1) If she does (c) or (d) it is a huge waste of finance as both visas are expensive in their own right.

2) If she does (a), does that give her any rights to continue her studies and part time work or does she need to stop because her student visa is voided?

I'm just trying to help these guys out. They're a good couple. She's legitimately been here for over 4 years and they've met as a consequence of circumstance. They're serious in their relationship but their story is vastly different to mine and so I don't really know how to advise them to proceed. 

I'd love to hear the input of others. 

Thanks.