She should try to see a dermatologist and get a different medication. Not all medications work for everyone, or they wouldn't need so many of them. Has she tried other medications? Birth control pills? Retin-A?
How bad is her acne? If it is cystic and causing scaring, she may consider Accutane. The side-effects aren't anything to sneeze at, but the results speak for themselves. I used it more than 6 years ago and my skin is still clear.
Even while using an acne medication, she needs to make sure to avoid things that will clog her pores. Tell her to only use products that say non-comedogenic or "won't clog pores"--"oil free" isn't good enough. Even after the Accutane, if I use regular products on my face, I get breakouts. Also, tell her not to use heavy makeup (I know it's hard not to when you want to cover things) and to clean her face no more than twice a day.
If she wants to get her skin clear for the wedding (who wouldn't?), tell her to ask the dermatologist about laser treatments. They are kind of expensive and don't last very long (a month, I think), but they would help clear things up for the big event.
I hope she finds something that works for her. Tell her not to give up on it.