I went through something similar after a long layoff, though not 30 pounds, and the hardest part for me was exactly that — my body kept trying to drop into my old stance and my elbow just would not sit where it used to. What helped me was stopping trying to force the old form and opening my stance up a little instead. I moved my back foot out a touch and let my chest turn a bit more, so my elbow had room and I was not jamming it into my side on the backstroke. It felt strange for a week or two, but my stroke straightened out once I stopped fighting it. I would work on that before rebuilding everything — get the stance comfortable first, then let the muscle memory catch up to the new shape. And yes, getting moving again helps, but you do not have to wait until you are back to your old weight to play well.