YTA. Fellow Australian here and whooo boy you are channeling some old school Botany Bay Penal Colony vibes because that is some harsh treatment there.

I agree with the other commenters who mentioned how excited you seem to be kicking your daughter out. Do you hate her for some reason? Do you have a need to enact an overly strict authoritarian role to big yourself up for some reason? Why would you need to involve other family members in this like you mentioned? Do you feel like having her around after this would be a constant reminder of having failed her or having failed as a parent in some way and that's why you want her gone?

Your pride seems very important to you but part of being a good parent is putting aside your own feelings and helping a child with life's struggles. Why did she steal the heirloom? Does she have kleptomania or some other kind of disorder? Is she in trouble and needs money but is too afraid to ask for it from you (with seemingly good reason)?

This isn't a special case, no matter what you think. My brother stole from my mother to finance his drug habit as a teenager and she didn't kick him out, she got him help. Lots of kids steal from parents, some big and some small. But the majority don't react like this. Not after having forged 18 years of relationship with a child. I think there's more to the story OP.