Try not to feel let down. Maybe you can do dog walking for other dogs, too.
I don't know a lot about Aussies, but I think that they are similar to border collies in temperament and energy. I raised a border collie from age 2 months. Although he was smart and learned many things at an early age, self restraint and compliance with requests/commands were definitely not his strong points as a puppy. He was too full of energy and playfulness for any self restraint.
But, once he reached one year old, he got much better. He not only cooperated, but looked for ways to be cooperative and helpful, just in order to please us. So I wonder how much good it does to try to train a dog like that in obedience while they are still puppies so full of excess energy.
We lived in a city with a fenced in yard so he got a little free run time there, but he sure enjoyed free runs across open fields in the country when we drove him out of the city to do that.
Developing a bond with him as part of the family did a lot to encourage his instinct to please us as he matured. Made it easy to get him to respond to commands like "No" and "stay, sit," etc. He became a well behaved guy with no outside training help.
But, as you said, it is her dog so she gets to decide how to handle him. Perhaps you can enjoy the company and affection of other dogs by taking other ones for walks.
Hang in there.