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Hill's Science diet makes a prescription food called y/d for hyperthyroid cats. Sometimes, cats don't need the methimazole if they eat this food, but that will need to be discussed with your vet.
In general, any soft food by a major company, that is high in protein and low in carbohydrates is good for hyperthyroid cats. Wellness CORE is high in protein and I used to feed it to my hyperthyroid cat that was also diabetic.
It may be necessary to have Molly's blood tested to see her thyroid levels and her medication may need to be adjusted.
Don't mix the medication in with the food, or that may be what's putting her off the food. If you can get some plain jarred baby food chicken containing NO onion or garlic, like Beechnut Stage 1 Chicken, crush the medication with the back of a metal spoon and add it to a tablespoon of the baby food and either feed it to her with your finger or put it on a flat small plate or in her bowl; if she likes the taste, you can offer more baby food. Since it's only chicken, it's full of protein. However, this can't be her only diet, because she needs the nutrients in cat food to maintain her health.
She may have trouble climbing the stairs now, because she's a senior, she may have a touch of arthritis and hyperthyroidism causes muscle wasting. Try to keep all her 'essentials' on one level of the house, where she doesn't have to climb stairs, like her food/water and litterbox.
If she hasn't seen the vet in a while for a check on her thyroid level, that should be your first step, in addition to finding a high quality wet food which is high in protein and low in carbohydrates.
I hope all will be well with your Molly!
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