Thank you for your replies everyone! She's turned out 24/7, has hay put out every couple days (more so now the grass is less) and has a feed (chaff, a mix and some oats).
I've just bought some toys for her, as there's not much to do in the field, and she doesn't enjoy running.
Can wind sucking be dangerous (other than maybe causing mouth ulcers and abscesses) I always thought cribbing caused the ulcers, rather than was a result of ulcers, but I will get her checked out.
Apparently she did when she was at the racing stables she was at, so my guess is she was either bored and learned it, copied another horse, or like some believe, it could be common to the breed (tb). Who knows? If it can't cause her serious problems, then I'm not too worried about her doing it (she's not a die hard cribber, I just don't like her doing it if it will harm her.)