Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl's bark suddenly sounds different. I can understand that you are concerned.
How is she behaving otherwise?
Is she bright, alert and happy, eating, drinking and eliminating normally? Or does she seem lethargic with a decreased appetite?
Any recent trips to the kennel, groomer, dog park or obedience classes?
Had she been barking quite a bit recently before this began?
A change in bark can be due to a sore throat. Too much barking, or exposure to other dogs and a possible respiratory infection could explain her change in bark. As long as she is eating, drinking and eliminating normally and seems bright and alert you can give her time and see if she comes along. It sounds like this has already been done and she is worsening with time.
Other reasons for a change in her bark can be neurologic. That means that if the nerves to her larynx are damaged somehow or not working properly then her bark could change.
Dogs with laryngeal paralysis will have a different bark. Laryngeal paralysis is often due to damage to the nerves to her larynx from trauma to her neck and the nerves in it when she pulls on her collar/leash when walking.
Other possible nerve related causes, but less common, are secondary to hypothyroidism, primary nerve diseases such as myasthenia gravis, and tick bite fever.
Very rarely this could be related to a tumor.
Since her symptoms aren't improving then it is time for another veterinary examination and probably blood tests to look for hypothyroidism, tick borne diseases, myasthenia gravis, and low blood calcium, and perhaps a scope to evaluate her larynx function as well as look for a polyp or mass.
Please let me know if you have any further questions.