Linda, I second what mammaK wrote almost exactly. I have some extensive experience keeping older horses without teeth. I don't know where your lady stands as far as dental health, but you can't go wrong starting out with a diet that mammaK spelled out and that will work well with or without teeth - just soak it first if in doubt and you should be fine. If you know for a fact her teeth are fine, give her an endless supply of this years cut hay. In fact, the only thing I did differently was I fed Triple Crown senior soaked instead of SafeChoice - only b/c I could get my hands on it easier.
I don't know anything about the feed you mentioned - haven't heard of it but that doesn't mean it isn't any good.
Horses are high maintenance and expensive when they get older and skinny - I think that is just how it is. It is one helluva commitment in so many ways to try to bring one back to condition - kudos to you for taking an interest in this mare and giving your heart and soul to give her a home!