Praise be to Allah.
The view of the majority of scholars is that it is not allowed to wipe over sheer socks or stockings, and that this concession is allowed only in the case of thick socks.
See the answer to question no. 228222.
If these stockings are light and what is beneath them can be seen, then the more correct view is that it is not permissible to wipe over them.
But if they are needed for medical purposes, and it is difficult to take them off every time one does wudoo’, then the individual may do wudoo’ before putting them on, then he or she should put a thick socks over them, then when needing to do wudoo’, he or she may wipe over the thick socks until he or she takes them off, or the period during which wiping over the socks is allowed comes to an end.
If he or she is not able to do that, and taking off the compression socks is something that will cause harm or delay recovery, then the matter comes under the ruling on wearing a cast, so he or she should wipe over all of it from top to bottom, which is the place which is required to be washed.
See the answer to question no. 192736.
If your wife takes the stockings off at night, she should do wudoo’ when she wants to pray Fajr, then put the compression stockings on, then put on thick socks over them, then wipe over the socks, as the ruling on wiping will apply to the socks and not to the stockings that are worn under them. Then when night comes, she may take off both the stockings and the socks, then when she wants to do wudoo’ for Fajr (on the following day), she should do the same thing, and so on.
I put this question to our Shaykh, ‘Abd ar-Rahmaan al-Barraak, may Allah preserve him, and he said that these stockings come under two rulings:
In one way they resemble a cast, because they are worn for an essential need, and in another way, they resemble socks. In my view, she may wipe over the part of the foot that it is required to wash, and regard them as being like the khuffayn (leather socks or slippers) in terms of the time-frame (within which it is permissible to wipe over the socks). They should also be put on when in a state of purity (i.e., after doing wudoo’).
And Allah knows best.