Any redness and pain like this is not something to fool with. If it is shingles, she still can get evaluated and treated. I hope by now she is feeling better. DVTs, (blood clots) are something to always be concerned about if redness is around the area. If there is any swelling than this is even more important to consider. As a sister to a sister who has had blood clots including in her legs, I still have to err on the side of caution. Please, have your mom get evaluated by her doctor.
sounds like shingles...its a form of chicken pox.
If she has not already, I believe she needs to go to the hospital. This could be something serious. Please try to convince her to go, you need to be concerned about things like blockages and such. Better to be safe than sorry.
Peace