Thank you for waiting. As you already know, it's crucial to get the temperatures up. A temp of 90*F is cool enough to lead to lethargy, but that is not brumation. Even during brumation, they need to be warm enough. If you decide she is brumating, she will require some special care. Their bodies slow down in response to the shorter days of winter, even when they live in our houses. During brumation, you shouldn't feed any live prey, but make fresh greens available. Once a week, take her out for a soak to keep her hydrated. Supervise the bath carefully since she is sluggish. As the days grow longer again, she should come out of this.
However, I don't think she is brumating. Start by getting the temperatures up to the proper level. A runny stool can be caused by parasites, illness, or a partial blockage. Crushed walnut is notorious for causing blockages. When there is a partial blockage, only very runny stools can pass through. I'll give you a first aid measure to take. If she is not blocked, this measure will not hurt her. Get some prune baby food. Drop a small dollop right on the end of her snout. Many times, they will lick it off by reflex. If she does, wait one hour before taking the next step. If she won't eat the prunes, just proceed. Buy some Pedialyte (yes, the kind for human infants), and prepare a shallow warm bath consisting of 1/2 warm water and 1/2 Pedialyte. Soak your dragon for about 20 to 30 minutes. After the first 10 minutes, with her still in the water, gently massage her underside from front to vent for an additional 10 minutes. That may be enough to help her pass some feces. Try to get her to swim while she's in the water, as that can help, too. Be sure to supervise closely.
I would get rid of the walnut right away. You can use paper towels as substrate until you can get something safer.
After you take all of the above measures, you may see a rapid improvement. If you don't, it would be best to schedule a vet appointment. When you go, take along a sample of her droppings to be checked for parasites. This link will take you to a directory of reptile vets:
Once the vet examines your beardie, checks for parasites, and possibly does blood work, you'll know if she's ill or if she's brumating. It can be really difficult to differentiate, but I am concerned because of the runny droppings. That isn't a normal part of brumation.
If you have more questions, just let me know by clicking on REPLY. I hope your dragon will be fine.
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