My Thai Gf has visited on Australia on Tourist Visa for 2 weeks in 2014,   3 months 2016 until Jan 2017,   3 months June to Sept 2017,  and recently returned to Bkk to apply for a further Visa. Yesterday she was called by the Australian Embassy informing her that as she is re-applying in under one month of returning to Thailand, she will have to submit a medical report within seven days... from a hospital to be nominated by the Embassy when she visits the Embassy in the next few days. She was also told that she will not get another Tourist Visa in the New Year.     Previously she has used an Agent to lodge Applications.   This time she lodged the Application herself with VFS.    Is this all 'Normal'.     Thankyou in advance for constructive comments and advice.

There is no limit on the number of tourist visas she can get.  

I don't believe there is any limit on how quickly you can apply for another visa either, however yes my girl has been told that she was "applying a bit too soon" and they "liked" to see a similar time back in Thailand as she had spent in Australia.  Obviously it starts to look dodgy when you try to stay 9 months in Australia over a year claiming to be a genuine tourist.    

Did she apply for a 6 month this time instead of 3? 

It's discretionary. If she starts to resemble a resident rather than a tourist then they'll expect her to apply for a resident visa - think marriage, living in Australia...

The medical is because she ticked the 6 month or 12 month box