welcome to the forum

We support each other here at NT.
I am sorry that your Mom is having this issue. There could be many reasons that your Mom is having the heat surges. I am glad she went for a work up with a doctor.
Please read/look over, the top section of the RSD/CRPS information posts/blogs. It may give you an insight to what RSD/CRPS is, and how it manifests and progresses.
I am not a doctor, and would not presume to diagnose the culprit that has entered your Mom's life(health).
I am sorry that your Mom, you, and your family have no answers since the workup that was completed on your Mom.
Sincerely,