If you are in the USA, there is a brand of deodorant available in all drugstores called "Secret" which really really works!
They have a variety of different types of deodorant, the creme, solid stick, spray etc., and they also have a new one "Secret Clinical Strength" that is for really problematic perspiration - which may be helpful for your friend (see website below).
This particular brand of deodorant seems to work better than any other, but please be aware of the downside...the stronger deodorants tend to contain more chemicals so you have to make an informed decision if this is less important than your need for a good deodorant!!
I would definitely recommend this though, it has helped a lot of people I know who had embarrassing sweat problems, and they also have some very nice different fragrances to choose from, it's also not very expensive which helps :-))
There are other prescription deodorants you can get from your Dr and some pharmacists, but these are generally only for very severe cases as they can stop you sweating completely and for most people this is not good as you need to sweat to flush out toxins. However, if your friend still finds no remedy from the drugstore brands she should consult her Doctor to see about a further treatment....
Hope this helps :-)