I have delt with this back home in California. I found the lump on her chest , it was as bug as a small apple. Warm compress as someone suggested . Once the skin is thin enough to lance it easily , you may do so , make a small opening near the bottom area to allow drainage , not to small that it wont continue draining and you cant get a syringe in to clean it , but not too big that its a huge hole ... Once its drained she will feel a lot better . We rinced it with distilled wated then betodine that can be used inside wounds with a syringe , lots or syringing with Betodine, there is a red labled one and a blue labled one , one is for inside and one for outside the wound , and it was diluted with warm water . I dont remember bandaging it up , maybe because of the position... I do remember having to re open it every day as it would stick together and not continue draining . It was 10 years ago so I dont remember shots , but possibly meds in pill form, I just did the washing 3 times a day . All horses ran together in a free herd , no one else got it , and I learned that it is a bacteria living in soil... Everything was over with in a few weeks , and horsey was good as new ... Dont worry , everything will be fine , its just a small set back and a bit of extra work and TLC : ) sorry that your going through this though , its never fun to watch your loved one go through an illness.