Rachael

Hi my sister who lives in Australia has sent over a gift for my new baby and one for my toddler, valued at $80 and addressed to both of them, and I am being told I can’t receive this parcel for them until I pay £18.79? She paid $80 for post it already so I don’t understand why I’m having to pay something for VAT? When she would have paid tax on tbe items in Australia how can I be charged to receive a gift for my children ?