If she'a already booked the flights the customary added charges for luggage, credit card etc. will already have been paid. The huge danger with Ryanair is that you MUST check in online before leaving for the airport. If you turn up without doing so there is a huge "fine".
I've flown numerous times with Ryanair and they are fine, as long as you abide by their 'rules'. You must make sure that luggage is booked both ways for both of you before you get to the airport. And do print off your own boarding cards.