Some people do send out wedding invites about 6 weeks prior. My friend did that but she also had told people who would have to travel that they were invited and gave details so they could book flights or time off work at least 6 months prior.

What I suggest is when you talk to her next, simply ask if the wedding invites have gone out yet. If she says yes and nothing else, then you know you are not invited. It gives her an opening to say either nothing or make her realise that you have not received it and Aust Post has lost it (not unusual! I have had 2 go missing).