(I know nothing about thyroids or this medication)
Why is her losing weight relevant?
Does she not like that she has gained the weight and wants to lose it?
How do her pants fit?
Is the number on the scale actually what matters to her?
If the number on the scale doesn't matter to her and the doctor said this experience is normal, then just keep on making strength progress. I really don't see the issue here. Perhaps you could illustrate for me what the problem is.