The best idea is to act as though you know nothing. If she asks, say that you saw her name (to file it) but didn't read it as you didn't want to know what it said as it was confidential and would put you in an awkward position, (as it has.) Your friend's mum has a right to know and will be likely to find out very soon anyway but it can't come from you because it is the doctor's duty, no one elses, to tell her. The best thing you can do is help your friend and think of her. If you breach confidentiality rules you could lose your job and your friend. Try not to worry, its a terrible situation for all involved, but for ethical and legal reasons, its probably best that you stay out of it.