Brief Answer:
We shall try to find the cause.

Detailed Answer:
Hi.
Thanks for your query.
To recapitulate: Daughter had tonsillectomy 6 months ago - constantly tastes a bitter sweet metallic taste - which ruins all flavors of any types of food - not improved but gotten worse - wants suggestions...

Please give additional information:
What is the age of your daughter?
Has her taste-function study been done in a proper way?
Is there anything that she has consumed like any other preparations like food supplements or odd foods and beverages?

I would advise you the following:
First of all to get a very proper examination and clinical evaluation by an ENT Surgeon and Pediatrician, particularly for evaluation of the Parotid and the Submandibular salivary glands as diseases of these can affect the taste the way she has been affected.
Since she has constant bitter sweet metallic taste, means she has not lost the taste function.
Such an alteration of taste is not a known complication of tonsillectomy at all.
- Watch for the medicines, foods, something unusual she is consuming. Such things or their metabolites can be secreted through saliva and cause altered taste.
An opinion of a Neurologist whether some neurological problems can cause such problem.

I hope this answer helps us to get a diagnosis, please feel free to give me the feedback and ask relevant queries if you feel that there is a gap of communication.

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