Spend some time composing a letter that reflects how much she’s always been in your thoughts, your open disdain for your sisters actions and your expectations from any contact she might feel to initiate.
Include some photos of y’all, address, phone, email.
Then comes the hard part. You wait. Patiently. Until she’s comfortable enough to initiate contact. And when she does, even if it’s years from now, be sensitive to moving forward at a pace she finds comfortable. Go slowly.
Wishing you the greatest good luck with your adventure!