In my personal opinion, from experience, your main problem here is that your tank is WAY TOO SMALL!!! I understand she is only 6 inches and that your husband is building an enclosure for her, but a 2 feet by 1 foot tank is WAY TOO SMALL for any Bearded Dragon, even a hatchling, not because of the available space inside it, but rather because it is impossible to have a temperature gradient of any kind inside it. You say she is "always laying on the "cool" side", but the fact of the matter is that your tank size isn't really allowing for a cool side at all. It's too close to the side with the basking light. So it's become a vicious cycle for your beardie-she won't bask under the light because she's already too hot/over heating on the "cool side", as already mentioned by someone else, and not basking under the light isn't allowing her to absorb enough UVB for enough hours each day, which doesn't allow her to process her calcium, D3, and all other nutrition, which can result in a lack of appetite, bone density issues, etc. This is the most important time of her life to get adequate nutrition and calcium so that she will properly grow...
I don't know how soon your husband will have her enclosure ready, but it cannot be soon enough. I'm guessing you will see a huge difference in her as soon as you get her out of that tiny tank, as it is essentially an oven that really is "cooking her", as already said...
