Sorry to read this, and believe Anna's advice is very good.
My feelings are like handling a baby...if they don't act sick (and you said she is not lame or stiff and running around like a nut!), I would go slow. The first thing I'd start is a weight reduction to help reduce the weight she is carrying. Over time, you may see this move forward quite a bit to help solve the problem, especially if she's considerably overweight. Gaining too much weight is also a slow process, so perhaps the continued added weight over a long period has slowly irritated the hocks into swelling. I would hope some weight loss would be helpful -- and certainly if you have to move forward with vet care, she'll be more able to get the care she may need if she's in "good" weight -- not overweight.
It's so hard to see all that "fluffy horses" go through and note all the changes. But it's good you saw this now.
Just my opinion, but waiting -- with some weight loss may be a good first step both financially and for her health.
Keep us posted.