I do not know about that airline, however UK airlines' policy is to ground any pregnant crew as soon as she declares it. I got grounded at 4weeks pregnant!!
I think you should look into it, it sounds really strange to me...
Besides once she's grounded she can always get a doctor's certificate to have her weekly hours/days reduced even to zero if needed, and the company cannot say anything! I had some problems too in the first half of my pregnancy and had my days reduced to 3 and then 2 per week. I was not supposed to do shifts either. It's also my company's policy that if you live more than 90minutes (I think) from your base they have to find an appropriate place near your home for you to work at and failing that they are obliged to keep paying you but you're not expected to go to work for grounded duties!!
I really think there's something wrong with what that company has told your wife, although I do not know if CAA rules apply to a foreign company, even when based in the UK. But you can always give them a ring and find out!
If nothing else works I would get a doctor's certificate for a pregnancy "at risk" and just be on sick leave till she starts maternity leave.
Good luck with everything, I hope your wife will have a smooth pregnancy from now on! xx
FBW
(yes, I'm still bloody waiting....
)