Well I'm not sure what the actual problem was but eventually managed online check in and allocated seats but unable to print boarding passes - website advised to check in at the airport and get them printed at the airport. Joined the large queue at KLM Desk but noticed some people being directed to Priority Check In as they only had Carry On Bags - so she joined that queue and was checked in with Boarding Passes within 5 minutes. So hopefully hassle free out to Houston but there is always the return which is next week - Houston Hobby - Atlanta - Paris CDG - Manchester. I did notice a direct flight on the departures board to Houston with Singapore Airlines but assume she didn't book that one as prohibitively expensive.