Yup, high heels are a killer for good posture and put A LOT of pressure on the lower back and feet. Worn too often they also shorten the archilles, making it hard to wear flatter shoes. There is truckloads of info about this and I suspect the reason that you don't find any on this site is not many of the t-men wear stilettos.
The plus side to them is that they are great for building excellent calf muscles, look hella sexy and don't normally cause any problems if you don't wear them all the time.
If however she is getting a lot of pain from just a couple of nights a week, there may be some underlying postural/back problems that the heels are exacerbating. Seeing an osteopath/chiropractor may be a good idea for her.