They won't, or shouldn't get through customs. I'm amazed that an Australian would ask you to send seeds of any description knowing that all mail into the country is screened for such things. Anyway, I'm sure I've seen Rudbeckia Golsturm in plant catalogues here, but that doesn't mean it isn't invasive. A plant can be a weed in one state and well behaved in another.
Thanks for your concern, it's a pity your friend/relative here doesn't share it.

The request was through GW. The lady who asked for the seeds admired the flowers in a posted photo, I am sure she didn't realise that they might be a danger ! Here they are a normal part of our cottage gardens. Thankyou so much for setting me straight , I will let her know they aren't a good idea, Cheers M

I have this plant in the garden and it hasn't self seeded even in Marysville where it is quite cold. The seed needs cold stratification to germinate and is not that easy. It is not a prohibited import as seed.

Thankyou for responding lomatia, maybe it would be better to advise my friend as to where she might find the seeds or plants in Australia. Any suggestions? M

The plants are sometimes available in herb tubes (3 inch) at nurseries. I have also seen them at Bunnings in slightly larger square pots. I've forgotten the name - something like fillers or bloomers?