Hoping she gets well
Hyperthyroidism is no longer a challenge for medicine, so she will be fine with treatment.
The right treatment depends on the results of her investigation but I can't appreciate that because I'm not Spanish, hehe but her specialist knows better.
Treatment might range from medications to surgery (thyroidectomy) but she will be fine.
It's really not that hyperthyroidism makes it unable for the body to regulate the glycemic level but it's that hyperthyroidism causes increase in metabolism thereby increasing the glycemic level of the body as glucose are released in excessive amounts