Nearly three legged at the trot is no-ones definition of "mildly lame" and actually constitutes a grade III of IV lameness, so "very lame" is actually the term we are looking for. Were the horse in the wild it would have been something's lunch by now. There is no way in hell, also, that Bute would mask this.
While it's great that you think it's okay for horses to live in pain, I don't. When a horse is 20+ and arthritic, okay, and only if it's managed, but to let them live with a severe, crippling injury and just think nothing about it is neglectful and abusive. There is something that can be done by a vet to this horse to make her more comfortable and possibly even heal and live to walk, trot and canter without having to limp like the dickens to get around. Not at least calling a vet and getting a diagnosis is neglectful. Were this a child, unable to run because of injury and the parents did nothing about it, how fast do you think that kid would be removed from their care.
And I know that people in this country don't give a **** about obesity, but it is a huge health risk and IMO also neglectful to let your horse, or your kids, get that obese. There are so many health issues related to obesity that can be fixed by one of two things, cutting back rations and/or a grazing muzzle - both of which will actually save you money.
Anyways, if the authorities haven't been called yet, they still should be called. Neglecting an animal in so much pain from an injury that it can't jog is abuse, and the BO needs what's coming if s/he is going to let a horse like that founder and die. I give the horse maybe another month before the obesity and overloading of the front legs end up in a severe bout of laminitis, which is likely the ultimate demise of the horse.
ANd one last point, to Cherie. Horses are not inexpensive and they hurt themselves. People unwilling to accept this and pay money for vet bills, and instead chuck the horse in a field or stall and go "LALALALALALA" as if they don't see the 3 legged gimping should not have horses, period. They should NOT be allowed to deteriorate and are in far more pain than you realize before they begin to deteriorate. It's great that you are in so much pain, really, so you must have a great understanding of how a horse feels. Next time you go to the doctor, don't talk, don't point and let him figure out where you hurt and what meds to give you based on gait analysis (that means running), x-rays and palpation. And then after a few diagnosis and (wrong) courses of treatment tell me how it feels to be a horse in severe enough pain that they are Grade III lame.
They say money doesn't buy happiness -- well happiness doesn't buy horses!