At 5'5", your body is trying to tell you that it doesn't want to lose any more weight. And that it is putting on muscle.

As you note yourself, the legs are the LAST things to change shape. I think you need to be more patient. Nobody ever said that Atkins plan was for fast weight loss. And the body keeps on changing for 6 months and more after you have lost the weight. You are very close to your goal and that last few pounds to a reasonable 125 will take a longer time. Use the months to learn to eat LC so you won't regain by stopping this way of eating.

But you are't putting on fat. If you are gaining, you are probably holding some water right now - TOM or salty food or weather or infection or stress (including stressing about making yourself lose pounds). You don't put on 2 pounds of fat overnight, but you can put on 5 pounds of water from one day to the next.

Patience. You didn't gain in a few months, and you won't lose and be a "finished product" in a few months. Keep on LCinguntil next December and see how things have changed. Or you could just continue to drive yourself nuts by making unreasonable demands of your body.