I agree with AnnieBrook.
I was 38 and overweight with hypothyroidism when I got pregnant with my now 13-month old son.
Healthy eating and cutting packaged processed foods and carbs from grains, white potatoes and refined sugar plus staying active helped prevent gestational diabetes during my 40w6d pregnancy. I didnt lose weight but I only gained a total of 15 pounds throughout my pregnancy.
I pray all is and remains well with your mom.
Bright blessings!
Specifically she should cut the carbs. Fats and proteins are fine, but carbs should go. Sugars, refined white flour, potatoes, and like that, can up the body sugar and make it really hard to lose weight.
Eating heathy will go a long way. Being overweight puts her at risk for gestation diabetes. Thyroid can cause miscarriage early on but as long as she is properly medicated and monitored it shouldn't be a problem, and since shes already 3 months it sounds like the Dr has it under control. The best thing she can do is eat healthy and light activity like walking. I'm sure everything will be just fine.