How to get my niece to grow up?

My niece is 17, she turns 18 in early October and is planning on leaving home after Christmas and getting her own apartment with a friend.

I have come down to help pack (without being asked keep in mind) and I told her to throw her teddies and dolls in the garbage and she refuses, I tried hiding them and planned to dispose of them but she found out and has kept them in her bedroom, she plans to keep them, I have told her she is far too old to have a teddy bear on her bed and she says "I don't care what you think of me" I am shocked! She is nearly an adult and she she won't grow up!

What can I do? You can't bring teddies and dolls with you! I HATE TEDDIES!

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