Volt benefit applied to my mobile but not my wife's

After a recent holiday my wife and I discovered that while I could use the Volt benefit O2 bolt-on Travel Inclusive Zone, she couldn't and ended up incurring a charge for using data outside the normal roaming zone. Our Virgin account is in my name because we couldn't open it as a 'joint' account when we first signed-up, many years ago. We both had Virgin mobiles which transferred to O2 in the big switchover and the Volt extras only seem to apply to my mobile. Is there any way my wife's mobile can be included for her to gain the Volt extra roaming benefit?