I am very sorry to hear that your girl is making odd movements with her mouth after looking at water today and not eating or drinking for the last 3 days.
This can be a sign of nausea but it can also be a sign of oral pain due to an infected tooth or a foreign body caught under her tongue, on the roof of her mouth or in the back of her throat. Sometimes it is a sign of an oral tumor. Since she is an older girl nausea due to organ failure is possible.
I know that she has had a recent exam and is being treated for hyperthyroidism but I suspect that she now has another issue, perhaps a root piece from a broken tooth that can eventually lead to mouth pain and a jaw infection/inflammation, or a mass somewhere in her mouth.
This behavior can also be due to a nerve problem or temperomandibular joint disease that is making it difficult for her to control her tongue or close her mouth properly.
I would look in her mouth, if you can't look your veterinarian can take a very close look under sedation to find the problem. But if she will let you examine the inside her mouth closely for swelling, reddened areas or any sign or trauma or a foreign body, especially under her tongue.
If there aren't any obvious signs of anything wrong in her mouth you can give her an acid reducer to try and settle her stomach in case this is related to nausea. Either:
1) Pepcid-ac (famotidine) at a dose of one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours.
These will reduce stomach acid and should help settle her stomach. These are quite safe and can be used for several days if necessary.
Then offer a bland diet of 2/3 boiled, white, skinless chicken and 1/3 plain, boiled, white rice. Give small meals several times a day. If she eats well feed the bland diet for several days, then if she seems better start mixing in her regular diet and slowly convert her back over a period of 5 to 7 days.
If she is still unable to eat or drink, or she is pawing at her mouth then I recommend she see her veterinarian tonight or tomorrow as after 3 days serious dehydration is possible. If she continues not to eat an esophageal feeding tube should be placed until they can figure out why she cannot eat and drink so we don't get into trouble with hepatic lipidosis (fatty liver disease caused by overwhelming the liver with fats broken down for energy to live when they don't eat).
If her symptoms continue in spite of using an acid reducer and a bland diet then she should see her veterinarian for an examination, some blood tests to look for underlying metabolic disease, and probably sedation to look closely in her mouth and take dental radiographs.
Please let me know if you have any further questions.