It makes no difference. Your "stuff" is tied to your AppleID, not your SIM. Backup your phones to iCloud. Then go to Settings > General > Reset and select Erase all Content and Settings. When you set up the new phone you'll enter your iCloud credentials and set up the phone with your stuff. When she sets up her 'new' X she will put in her credentials and set up the phone with her stuff. You will need to tell the phone company so that her number can be associated with the X and yours with the XS.