I know the Mt Lofty running track. I was thinking more of the actual botanic gardens up there. You can pretty much drive in and park (from memory), and the walk through the park itself is not all that onerous, but there are many nice locations to shoot from.

I guess if the girl has contacted you, then it's her show, and she would have to give you some more direction as to what she wants from this shoot too. There are some nice areas around Stirling and Hahndorf in the Hills too.

Good luck - hope it goes well for you.