As Serfty mentioned, so long as they have photo id to check in at a counter or can do OLCI and print out their own BP, Aust dom flights are the easiest ones to use, and are not like other airlines overseas.
I have booked and paid for flights with my card for my parents (I don't fly with them), they sometimes fly Jetstar and I print out their BPs for them, with these BPs they just scan that at the gate and they are good to get onto the flight.
Edit: I have been having a bit of trouble getting the VA system to book for myself, using my own card of late, I would say its more so the system, rather than the card, but you can try booking your relative at http://www.virginaustralia.com.
Seems that it gets stuck at the date stage.
On it (you might have done bookings on VA for yourself in the past), but on the booking system, you can tick a box or something that asks if you are flyer, you enter details of the flyer, and go through with the purchase.
If the relative has a VA FF account, you can remind them to bring along their VA FF card to get points and SC.