It can be done... your girl friend will need to show proof of ties in Laos...Home ownership, family, good job to return home to etc and you will also need to show similar as as you will need to show that you will support her while she is there.
To be honest I have never heard of a Laos girl being accepted by the Australian authorities and an agent can not do anymore than you can do as regards applying for said visa and the paperwork required is a nightmare....I have done a few applications for a few friends over the years and the 32 pages of docs and letters of invitation, bank statements etc does take time to get together....Anyway if you both qualify give it a go but in saying that I would not get your hopes up to much.