Hi Jollyc,
This happened at Xmas just gone when I booked an outward flight to the UK for my sister in her maiden name.We were flying home from a different airport & I realised my mistake when I went to book the return flight.(Booked the return in her married name.)I phoned the Ryanair customer desk & like Patou ,they told me if she had her marriage cert with her it would be ok.
So on the day,at check in,they did pick up on the difference in surname between passport & the name in which I booked the flight ,without any prompt from us.
My sister produced her marriage cert & all went off with out a glitch.No Hassle.
Hope the your experience is the same.