I have problems with both my thyroid and parathyroid. My calcium levels were just slightly low in the 7 range, when we discovered my parathyroids werent working due to damage during my thyroid being removed. Important : Ionized calcium or corrected calcium should be checked not just standard calcium.
Extreme Fatigue and brain fog was HUGE and still is for me although MUCH better since being treated with Calcitriol ( a presciption form of Vit d) along with vitamin D and calcium split up - 500 mg 2 times a day. (Shouldn't take more than that at once if parathryoid hormone not there as kidneys can't handle more than that). In addition, I am suffering from months of arm pain, although has lessened recently with me taking calcium 2 to 3 times a day. There is some great literature on the hypoparathyroidism association website ...which might search to find..unfortunately this year becoming paid site but may still be able to get to articles. If unable to get, I have much of it downloaded and would be glad to email to you. Its pretty rare and my experience is even endo's don't often understand it. I also deal with the thyroid problems so very difficult to sort out what goes to what. Hope that helps a little. Here is a portion of one of the leaflets...they recommend sharing with doctors etc..
Calcium levels and hypocalcemia
Calcium is an essential mineral which provides our body with the ‘electrical’ energy it needs for the smooth running of our nervous system and muscle contractions, including our heart. It also provides the strength and maintenance needed for healthy bones and teeth and is involved in the clotting process of our blood and our feeling of well being. Normally the calcium levels in our blood are automatically and precisely controlled by the actions of four very small, but blood rich parathyroid glands in the neck. In Hypoparathyroidism this automatic control is missing so when the calcium levels in our body begin to get low there will be insufficient ‘electrical’ charge for our nervous system or muscle contractions to work properly. The body will respond by sending out warning signals that blood calcium is getting low and we begin to develop symptoms of neuromuscular irritability called Hypocalcemia. Equally when the level of calcium in our blood is too high the body will send out signals.
Oops, I said Freet3 twice! (it's herTSH, Free t3 & Free t4 blood test that need to be checked)
You mentioned her parathyroid levels? Were her actual thyroid hormone levels checked? This would be more of the norm for a doctor to look at first. Her TSH, Freet3 and Freet3 levels are needed with the reference ranges. The fatigue, muscle/joint pain can all be symptoms of low available thyroid hormone in the body (HypOthyroid). I would encourage you to have her get additional testing for this FIRST.Keep us posted!