S4 sim card replacement

Hi,

My girlfriend's Galaxy S4 is completely dead. We have tried starting it in safe mode, we tried replacing the battery and the phone itself, not the battery, just gets hot every time. Will not start even in safe. The phone is old and she needs a new one anyway.
So I want to give her my S8 Active to use, however the SIM card in her S4 is the original version SIM, not a micro SIM or a nano which is needed in the S8.
Question is if I get a new nano SIM card how does her information (account info, current phone number, etc.) get on that card. Does the card have to come from AT&T with her information loaded on it already or can I go buy an AT&T nano SIM at Walmart and somehow get her information on there so she can use the S8?

Thanks
Bob