If the rosebush is doing very poorly and you fear that it will not make it through the winter, then I would transplant it right away. If it is doing okay but could be better, I would wait until very early Spring before the bush starts to leaf out and move her then. Either way, once moved to a new sunny location with better soils, water the rosebush in with some water that has both a good root stimulater and a product called Super Thrive mixed into the same water. Water the rosebush with a freshly mixed batch of such water the next 4 to 5 times she needs water. This will get her root zone going well and the super thrive also helps the rosebush deal with the shock and stress of transplanting. Here is a link to an article on this subject for you as well: https://www.gardeningknowhow.com/ornamental/flowers/roses/transplanting-roses.htm
