MariaAN

Unaccompanied minors for airlines are 14, 15, or 16 and under, depending on airline. You say she is under 18 but don't give and age. If she is over 15 she should be fine.
 
If she is a citizen of both countries then there is nothing needed for her to move and live in either one. She can live in either places as ling as she pleases.
 
The only issues that may be of concern is guardianship or custody issue because she is a minor. But that is not immigration related.

Thats all she needs.  At 16, no airline considers her an unaccompanied minor.  United will allow you to take her to the gate, but many airlines, like westjet for example, will not give a parent a gate pass.  Just some food for thought. 
My kid is 16 and I get a gate pass for pick up and drop off since they go through customs in Canada both ways. 

I just did mine last Friday. 
 
So I did not sign my form until I get there, but I knew some people around me did.  No one was really checking though.  The Immigration officer did say here're some pens, sign them and use this city (Philadelphia, PA - in my case) and date the signature that day (5/11/18) in my case.
 
I think you will be fine. Do not worry about it.  Enjoy it tomorrow, and congrats!