While I understand Rogers Comm not wanting to give you the persons information, I’m surprised they are unwilling to accept the phone to then forward it onward to the owner.
Sadly ‘Find My iPhone’ or the newer ‘Find My’ both require the owner has either another iPhone. iPad or Mac to run.
What you could try is see if Siri can help you! Ask it to call mom or dad see if it will call them, then explain you have their daughters phone.
Its possible she already got a replacement phone (insured) and it might even be a newer better phone! So she really dines’t want the old phone back! If she was lucky all her photos and other stuff are in iCloud so she didn’t loose anything.