I'm also confused by what you are saying with "She'll be dead in a few years anyway".. Is she up there in age or something? I can't remember if you said how old she is, but if she's in her late 20s, I wouldn't breed her in the first place.
And I agree with Crimson -- Every other person probably thought "One more horse can't hurt". That ends up being quite a few horses.
If you do ever breed her, your best bet would be to breed to her an Arabian stallion that complements her and fixes her flaws, not just some fugly animal that happens to be homozygous black. At least then the foal could be registered half-Arabian. You won't get much for colour though. The cream dilute doesn't exist in Arabians, so no buckskins, palominos, cremellos, or perlinos. If you want a buckskin or palomino, buy one.
And as for "mutts" -- One of my dogs is a mutt and he's probably the best dog I'll ever have, but he was probably an accidental puppy as his litter was just dumped on a doorstep when they were a few days old. But I DO NOT agree with "designer breeds" for any animal. It's ridiculous and destroying breed standards. Poodles do not need to be bred with everything just to get dogs that don't shed. Horses are the same way: If all you do is mix breeds, you're ruining breed standards.