How about letting her out but with a grazing muzzle instead? Hope I'm telling you something you already know here... regardless of how fat she is, how expensive the hay(I know, I'm an Aussie too), horses need near constant access to forage. Even going hungry for a few hours is very bad for them & if this is the case, your horse's behaviour may not just be boredom, but from pain of ulcers.
I think it was on the safergrass site or on Pete Ramey's site that there was a link for 'slow feeding'. Basically, the hay is put in a crate or such made from, or covered with weldmesh, and the horses have free access, but can only get tiny amounts at a time. There is also hardly any waste. That might be your answer if you have to lock her up.
The more exercise the better. Heard of Jaime Jackson's 'Paddock Paradise' system? I googled it & came up with a fair bit of info. Looks great, but I'm agisting & can't do it here...
Last edited by loosie; 11-19-2008 at 04:22 PM.