BUDHISM derail into Satanism.

[The Magic Pudding]

I thought a "sheila" was a girl human in Australia.

Ye it was a thing, it is more than a bit old now though.
I'm pretty sure I've never used the term and I don't think my contemporaries did but I know some guys of my fathers generation did.
If it is used now it would probably be by a comedian doing some thing long past its use buy date.

[Ali]

Isn't a "Sheila" a girl kangaroo?

No
I mean there could be a girl kangaroo called "Sheila," I don't know all their names but it isn't a general name like sow or mare.

I'm going to get a kangaroo, and name it Sheila. Then I'll (blank) it.