Wasnt sure whether to put this in immigration, but technically not a migrants visa... so mods, feel free to move if you see fit

My mum arrives on 20th Jan for a two month visit. She has her visitor visa which doesnt expire til 30th Jan (which she used last year for three months). My dad seems to think she can just apply for a new one whilst she's here but is that correct?

Not sure exactly what visa they come on, but I think it costs them about $20 and they apply online if that's any help...

Thanks