Where is she buying the iPhone from? Since you claim it's unlocked, sounds like either Apple or a seller on Kijiji. Obviously no IDs or account access issues will arise here.
Then she can buy a prepaid nano SIM from a Koodo shop or anywhere else they're sold ($20 + tax) and then bring it to you so you can activate it yourself. If she knows your login details then she could do this change herself in Self Serve but then you wouldn't be able to use it until the phone is in your possession.