Hello,
Welcome to HCM & thanks for asking your question.
I would like to tell you that 4000 IU of vitamin D will not cause any kind of weakness in arms, but in stead i guess weakness in her arms may be due to low levels of vitamin D and calcium.
Can you provide me some important details regarding your daughter, so that i can guide you in right direction. What is the age of your daughter? what are the last reports of vitamin D and calcium? i guess, she had undergone
thyroidectomy, so can you tell me if she is taking any kind of medications?
Sometimes, during thyroidectomy,
parathyroid glands which are present besides thyroid, are also removed unknowingly and that can lead to calcium imbalance, because PTH hormone is secreted from there. Function of parathyroid is to increase blood calcium levels and cause resorption of bone.
So i would recommend you to measure PTH levels in blood of your daughter and also want to add that take calcium tablet also along with vitamin D, as i guess your daughter is in growing phase.
Hope it will be helpful to your daughter's better health.