Help! I'm spongy and I can't get up!
I'm new to the forum, but if I can save this plant you'll be seeing more of me, I'm sure! This is sort of a long story but, for the sake of this poor plant, I hope you'll stick with me...
My Grandma Pat has had this desert rose as long as I can remember. She may not have had it my whole life (I'm 25) but dang near. (That was to give you an idea how old it is and why this is so important to me.) She passed away when I was 12 and, since then, various clueless relatives have just barely kept it alive. Well, my grandfather just had to move in with my uncle and the poor thing got deserted at the now vacant house. When I found it, it had been sitting in a completely dark room for *at least* one month. Not being watered, obviously. It had lost most of its leaves and several of the smaller stems. I brought it home in a panic. I took off all the brown bits and cleared the debris from the pot to prevent disease (I have some gardening experience, just not with this particular plant). The stems, all the way down to where the fancy shmancy caudex should be, are quite spongy. They're not as spongy now as they were when I first brought it home a few weeks ago, but still not firm. When I jiggle the base it feels unstable, like a plant with root rot would. But how would it get root rot without being watered? I've been watering it since I brought it home maybe two weeks ago, just tiny amounts every day, maybe 1/4 - 1/2 cup. I don't know if I should be because (and this is the essence of my question) if it is going into its dormant state watering could kill it but if it needs water then not watering it could kill it. I have to keep it inside because it's frosting here now, but I get terrible light in my house, I have it in the lightest room (attached picture is daylight, no artificial lights), but it is NNW facing, no direct sun. However, this particular plant has always been light deprived, in a relatively dim kitchen for 20 years. My dad said maybe I should prune it. He mentioned his mom cut it back to basically a stub at one point, which I can see from the scars, it was cut back to about 6 inches. As far as I remember, it has always been pretty much this leggy, but not droopy like you'll see in the picture. I've done a lot of Googling, to no avail, and my friend and I have brainstormed, but we don't usually grow anything we can't eat or use as medicine, so we're pretty clueless in this situation. Please tell me I'm not going to lose my grandma's plant! Thanks for any help you're able to give!