Hello Alli! There is still hope for your plant. You are right, your container is wrong for it. It must have drainage holes. I would pull out that plant, change the container with something with holes below or if you really love that container, drill holes below. With the soil, try to make it really well draining too. I use cactus and succulent mix which I get from HD or Lowes, then I even further add more perlite or pumice in it to really make it porous and well draining. These succulents hate to be in soaking wet conditions, they are not tropical plants that like moist soil a lot. During winter, they can take cool temps but have to keep them dry as much as possible.
Jade plants are very good at hoarding water in their stems and leaves. That is why you have to adjust watering as seasons change. Cold season typically requires less watering, just once a month will be okay at the most.
I would just remove all those dead looking leaves. You can trim those overgrown stems, each stem node and leaves has potential to form roots. Jade plant roots are not big and they are rather shallow growing, so they do not need very deep containers, unless the plant has grown later on into specimen sizes. Just lay the cut off parts on top of the soil, allow the cuttings to callus and you will see later it will form roots. At times, it may even try to form new leaves, before the roots. Then you can plant them. In my area, Jades are actively growing when our temps are mild and cool, so this time is still okay to try and root them when temps are between 65F to 75F. Just keep them in a warm, part shade for now while it tries to form new roots.
Try to position your plant later in a bright light area, otherwise it will etiolate, elongating its stems as it tries to reach for more light especially during winter when our daylight duration is quite shorter. When it is grown in more shade, the leaves turn deep green, if it gets ample light, it turns like apple greenish color. When it is cold stressed, the leaves turn reddish hues at the edges and as it gets more cold stressed the entire leaf can turn burgundy red. Too much cold temps can cause wind burn, that can make the tops get blackened leaves and tips. If it is not too far gone, it can bounce back quite well when temps warm up in Spring.
