I am the same as your wife. When I am too cold, the pain starts and I turn purple. When it is too hot and humid, I crumble like a wilted flower. And I always have to drink water constantly, I think this is due to my blood volume.
Weather is the key to how I am doing that day. It does make sense as the veins either dilate or constrict according to the weather.
Today I am having a blood draw and that will put me down. Luckily the nurse is coming to my house so I can immediately go lay on my inclined bed afterwards. Since I have been sleeping inclined, I can see my veins better in my hands and arms.
Your wife is not alone.