Hi Spencer.
Not sure about the thyroid issues, but constant high blood sugars do cause weight loss. It is essential that your Mum tries to reduce her blood sugar levels to as near normal as possible. How is her diet? She needs to test regularly to find out how different foods affect her levels, everyone is different, but very low carb seems to work for a lot of people. If her diet is already good, she may need additional meds, or a change in them. Good Luck, Mandy.