At the risk of being flamed...If it's "just" for the foaling experience, then I think you are breeding for the wrong reason...jmho. I know you've talked alot about her behavior and how difficult she's been to work with in the past, and along with her less than desirable conformation, and build, those are all traits that can be passed on to her foal...you are wanting an athletic foal, who can jump and do things mom can't do, but you've got to look at mom; if she can't do some of those things, do you honestly thing a foal out of her will be able to do them any better than her, no matter how nice the stallion you breed her too is? A stallion will only be able to improve so much on your baby...he's only half the picture, here...your mare is the other half.
Now if she had really desirable conformation; nice hip, good shoulder, good legs, etc, along with really nice temperment, THEN I would think about breeding her, regardless of her grade status, because then you would likely get a foal that has those desirable traits as well. However, because she doesn't have those, you are taking the chance of having a foal that has crappy conformation, and a hard to work with attitude...regardless of how lovely the stallion's confo and attitude is.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."