I would have suggested potting mix of 60 coarse gravel, pumice, and no vermiculite. or peat moss. You can also toss in small rocks, in Africa they grow on rocky hillsides between the rocks, and get fertilized by the leaves that they drop, or a stray goat or sheep, rabbit or rodent. it really can use full all day sun, and little care, but I notice the zone that you are in, and if you have high humidity and water, it may be in troube, because of the mix. I know how to save it, but it is drastic, and I'm afraid even to suggest it. I don't know what kind of soil mix is availabe for you to buy, and much more information is needed. Are you east of the Rocky's or West? This group will give you a lot of suggestions, and they are good. So go with it. Norma

If you can, take cuttings from a healthy portion of your jade, just in case. If the worst happens, you'd still have a piece of the original plant.

Yes, take cuttings from completely healthy parts of the plant. That way you can regrow this, if it dies entirely. Unfortunately, I have had the frustrating experience of watching a succulent die in stages like this. I don't think there's a whole lot else you can do now - I can't think of anything you need to use to seal cut pieces.

My recommendation would be, if your plant stabilizes or you are starting with cuttings, try taking it outside during the summer. I have various Crassulaceae (relatives of jades) that really struggle through the winter. If I didn't take them out in the summer to get them as happy as possible, I'm not sure they'd make it to May (this is when spring hits around here). Be careful of sunburn early in the season.

Any plant can be saved if not dead, and rotted. 'Jade' is a Crassula ovata. Sunburn is natures way of pruning the plants. The drastic way to save the whole plant it to cut it off at the base, (the soil line) put it in an empty pot, no soil, and set in partial shade. When you see roots forming, lift it up and fill the pot half full of soil, put in the roots and cover with soil, now don't water until you see new growth on leaves, start pulling it out further into the sun every week, in the spring water and fertilize regularly every week. Please don't be afraid to ask me questions if I did not explain that clearly, I don't express my self well when I write, as I have had a few strokes, but I will respond to questions. An established plant can handle cold down to 20F if the soil is dry.
Shorten any stems that hang down. Cut the top growth down, so it isn't top heavy, and remove any roots that don't look healthy. This is my drastic remedy. Norma