There are three things you need to prove to claim 15 point for sibling
1. Proof of PR/Citizenship status
2. Proof of physical residence
3. Proof of relationship
To show proof of siblings PR status you will have to submit scan of front and back of PR card. So yes, you have to wait till she receives her PR card.
To show proof of physical residence you can use rental agreement and utility bills. But you cannot use these to prove point 1 ( PR status).
So yes, please wait for her to receive her PR card.
Please refrain from providing misguided advice. The signed COPR is sufficient for proving PR status.