HiCustomer and thanks for getting back to me.
Based on your description of what is occurring, there are several possibilities that could explain your mare's condition. My first thought was a condition known as a carpal hygroma, which is basically a buildup of joint fluid normally on the front of the knee (carpus). There is normally no lameness associated with this condition and it usually has no long term negative effects. I have an older quarterhorse mare that has had hygromas on both of her knees for years with no ill effects. However as it seems as if you are beginning to see some signs of lameness there could be other possibilities as well. There is a good possibility that the swelling has been caused by some sort of trauma to her knee, resulting in inflammation within the carpal joint capsule, which in turn results in a buildup of joint fluid in the capsule itself, along with sensitivity. Another possibility would be the existence of a fracture within the joint, which of course can only be diagnosed with an x-ray. Unfortunately in your mare's case, without some additional diagnostics (x-ray, ultrasound and/or vet exam) it is extremely difficult to say what the exact problem is. What I would recommend is a daily dose of cold water therapy, which consists of letting cold water from a garden hose run on the swelling for at least 10-15 minutes. Following that, application of DMSO directly onto the swelling may be beneficial as well. You should be able to obtain DMSO at either your local feed/supply or drug store. Be sure to wear gloves when applying. As far as the bute, as this is a prescription drug and I have no way of examining your horse, I can not legally give you a dosing regimen as there is no patient/doctor relationship. I can say, however, that if you are to administer it, not to exceed one gram twice daily. If you can get ahold of the doctor who is opening a clinic in the near future, she or he may be able to give you specifics over the phone. Again, without being able to examine the swelling, I can't recommend or discourage a wrap at this point. If there is active swelling, inflammation of the possibility of infection, a wrap can be counterproductive. Your best bet is to try and keep her confined to a stall or small paddock to limit the amount of activity on the knee.
As far as her weight problem, be sure that she is up to date on her deworming, and try to have her teeth examined as soon as you are able, as these two factors are the major causes of weight loss in the horse.
I hope I've been of some help, and please let me know if you have any further questions.
Thank you, XXXXX XXXXX of luck!