HI,

Your heart goes through the floor when you get news like that, doesn't it? Especially when you thought things were going well. The great news is that it's completely possible to build up your supply, and it is pretty easy to do.
As you have already guessed, giving her both breasts at every feed is important - it will just about double her milk intake alone. Once she gets the hang of it you will find that she wants both breasts all the time. It's tried and true advice, but can you spend a few days really concentrating on feeding her? Put her in bed with you - send all the visitors away, get some magazines or DVDs you like and just feed her.
Her weight gains have been quite low previously - has the health nurse mentioned that? It would be an extremely good investment to see a good LC (there are plenty in Perth) and join your local ABA group.
BTW, milk "not being good enough quality" is a myth. It's all fine. Generally, it's just an intake thing - baby is not taking enough milk
Barb