
People don't, typically, take Thyronorm if they are hyperthyroid... Do you mean hypothyroid, instead?
If your mom has been overweight and had trouble losing weight, it could be normal for her to lose weight with a dosage increase; however, if she didn't need to lose weight and is losing too fast, it's possible that her dosage is too high.
Did they test her thyroid hormone levels before they increased her Thyronorm dosage? If so, can you post them for us to see?