How Do I Help Malnurished Bearded Dragon?

These are things you're going to have to do daily:

-Soak her in a mixture of 1/2 unflavored Pedialyte (this is a drink sold in the infant aisle at pretty much all grocery stores) and 1/2 warm water. Soak her for 20 minutes and make sure the water doesn't get too cold.

-Feed her a decent staple insect, I recommend dubia roaches. If you feed crickets, I would recommend pulling off their back legs as she is very weak and might have problems chasing her prey. Feed her once daily, preferably in the afternoon.

-For added nutrition (or if she isn't eating), make a mixture of chicken with chicken gravy baby food, any insect you prefer (although I recommend a few waxworms, Goliath worms, or butterworms as those are all high in fat), unflavored Pedialyte, water, and calcium with D3. Feed this to her by either using a clean Q-Tip or art Popsicle stick and putting a pea-sized glob on her snout. Typically they'll lick it off, but if she doesn't, you're going to have to feed it to her through a syringe.

-If you have a blender or food processor, blend (or process lol) dark greens like collard greens, dandelion greens, turnip greens, and romaine lettuce with some water. Feed this to her through a syringe.

Also, just make sure she has enough heat and a decent UVB bulb. I'm guessing you rescued her, and thank you for doing that. Feel free to ask me any questions, I'll be happy to answer :)

(Sorry if it's a boy and I just called it a she throughout this whole answer lol).