How's his coat looking? It could be depression but it seems as if he's losing weight too rapidly. I'm guessing he's extremely lethargic judging by his loss of appetite. How are his eyes? Gums? Teeth? I think the poor baby needs a full blood panel done. If she can't possibly pay for treatment, it's a good idea to know at least what is inflicting Little. By the way, in case this problem is hereditary, has she speutered the dogs yet (including Little)?

PRICE
An informal survey shows that for a routine blood chemistry panel the dog owner might expect to pay from $17.50 to over $60.00.
That's not too bad. 60$ per vet visit is half what we pay regularly.

Edited to add: Many shelters across America offer low-cost veterinary services. Ours does, and I'm sure you can find one in your area.