Before I get started, I'm aware it is down to poor management on my own behalf, and accept responsibility for not keeping on top of it. I have my excuses (permanently injured that has been recently troubling) but I try not to play on them when I know there can be more I can do to prevent. Out of sheer frustration I've turned here however, in hopes someone can guide me with how to slim my mare down.
Honey's basic situation is that due to my injury since Mar 09 she's been a pasture pony really. She gained weight that she lost over our last winter, but we had a killer of a spring, and she's the type to gain on the smell of grass. I have finally gotten my own electric unit, but of course, ran out of power to run it (board her at a DIY facility) and due to personal reasons have not had the money to power it back up until now. Penning her up is something I've always ran into problems with unless its electric, as she's a bit of a houdini or will break through when her eyes get the better of her. She's even been attacking the wooden posts lately, which I know is a sign of lacking fibre, but I'm not sure how to address this, when its one of those situations where you want her to lose weight, and only give her enough hay to keep her going daily, instead of giving her heaps and having her gain even more (which she does).
Since her exercise is limited to lunging at the moment, its not exactly the easiest situation to approach. I usually hard feed my horses year round as I like to get supplements and minerals into them, but I haven't for a few months, so could this be also down to the reason she's attacked the wooden posts? Normally she just gets chaff with her supplements and I'm thinking about changing her back to this rather than the hay which she normally only gets over winter as we have more than enough grass. She isn't in long grass at the moment and hasn't been for weeks now. She is wormed and has good teeth too.
Is there any thing I could be adding or changing to help her with her weight? She currently looks like this...

I'm trying to help her slim down so we can start riding work again, and after sitting up on her the other day and feeling like I was doing the splits, I've become very aware of how detrimental I've allowed her weight and health to reach.
Please help this guilty horse Mummy!
Thanks in advance!