Need medical advice

Five days ago my mare had developed a sudden inflammation in her neck, right behind her cheek. She doesn’t show any signs of pain or discomfort. The doctor said she just had bad blood circulation in the jugular vein due to the cold (we’re currently at the end of winter, the weather’s the warmest it’s been in 4 months), and he suspects she already had issues in the vein before we got her (9 months ago, in july).

He recommended we put hot water packs on the area, and we could potentially put some type of gel medicine to improve circulation (hasn’t told us the name yet 😓).

I just need advice on what this might be, and what I can do about it. I tried asking, but I dont understand why she would get an inflammation there specifically and why now of all times when it’s significantly warmer. Thank you!