I have heard of a charitable hospital at Meera Road ,Bhaktivedanta Hosptal run by Iskon group.
If they diagnose any thyroid
malignancy, then you may take her to Tata Memorial Hospital , Parel, Mumbai.
The above are only few leads. Kindly do your research on them before landing there as I left Mumbai in the year 2000.
Wishing you all the very best.
Dr Lt Cdr ASN Bhushan.