If the phone was purchased since December 1 2017, all she needs to do is buy the SIM from the US carrier of her choice. If purchased earlier, she simply needs to contact Telus and request her phone be unlocked. There is no charge for unlocking.
In addition to what @NFtoBC said, the phone may or may not be compatible with CDMA, so Verizon may not support it. AT&T, T-Mobile and many other carriers, should be fine. They generally ask you to enter the IMEI of your phone and you can do that from here.
If the device is SIM unlocked, most providers should work fine. Sprint and Verizon might be a bit more of an issue compatibility wise along with some of the old NVMO's, but as mentioned, T-Mobile, Metro by T-Mobile, Cricket, and WalMart's because it uses T-Mobile should be fine.
They WILL ask for your IMEI. I've done this. I've moved a Canadian unlocked phone to the US. More than one in fact, and an iPad. It was not acceptable for Verizon.
If the OP wants the answser, go onto the website, start the process of getting a "BYOD" plan and it will prompt you for that IMEI. This will answer your question 100%.
Been there, done that, got the Tshirt.
T-Mobile does not use the devices IMEI to restrict carrier features, so any unlocked compatible device with the correct APN settings will work with VoLTE on T-Mobile. WiFi Calling might be a little more complicated.