With the symptoms you list its time for a vet check up with her vet.
Two of the conditions that include increased hunger and thirst and weight loss are Diabetes which you can read about here
http://www.caninediabetes.org/
and Cushings disease an adrenal gland problem which you can read about here
http://marvistavet.com/html/body_cushing_s_disease.html
Other health issues such as intestinal parasites are of course also possibilities.
Its going to take an in person vet exam and possibly some blood work or other testing to find out what is going on with her.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics