Ugh, I feel bad for your girlfriend! My reading indicates that nerve issues are more likely to cause her symptoms. They call it neuropathic pain and the red color is common. Let me know what her doctor says.
Hello~You are on the right track by taking the B vitamins, they are the "Nerve vitamins" I would take a good, high-potency complete B complex, it is best to take them all together as they work best instead of taking just one B vitamin, such as B12 alone.
I also suggest seeing a chiropractor, she may have some misplaced vertebrae in her back causing some pain in that one leg, it doesn't always cause pain in both, especially if the pinched nerve is more on one side than the other.
I hope she feels better soon.