Hi guys, thank you for all your replies
Gluey, no I'm in England.
I read a lot about Gastric Ulcers last night, and she doesn't have any of the symptoms stated on all of the sites. However, I've read up on the prevention of them, and they also tie in with the prevention of cribbing - access to decent roughage, and smaller more frequent meals - which will mean the acid is digesting her food (not her stomach lining) and also give her something to do 24/7 so she's not bored.
I've started putting her hay in a net instead of chucking it out in the field in one chunk, meaning it take longer to eat, and makes her work for it. This morning I got there, and instead of finding her cribbing, I found her munching from the hay net. So maybe she was just bored, so I'm going to give her a net every night now.
I've also ordered her some toys, and they'll be getting here tomorrow or friday.
I think it's probably mostly due to her boredom, rather than ulcers, however, I've realised what I need to do to prevent ulcers, which is good, being as prevention is better than cure
Thank you for your help everybody