I'm bipolar and I don't think anyone could convince me that the visions, prophetic dreams and messages from voices are not real. Mainly because so many of them later turn out to be accurate. I too have peers and family that believe this is true as well, because they have seen it happen. I find that even though I recognize these as symptoms of a disease, like the audio hallucinations and voices, I can not convince my self that they do not exist, and I suppose having other people believe in their vlidity does not help me push them aside.
Granted, some of them are just silly, for instance I was instructed to take my safety shoes home from work for Christmas. I forgot, and worried about it a little, even though I understand these are just symptoms of a disease. But I've never been told anything that I'd consider harmful. Sometimes it just makes me mad when people try to deconstruct the prophecies. Everybody has at least one wierd belief in their life that other people may find ignorant or really strange. I bet you've got some too. If it aint broke, don't fix it. Unless your friend is being harmed by these things, I don't know if you should worry. If she is being made paranoid by visions of bad things, or warning messages that make her afraid to conduct her normal daily life, then she should talk to her therapist about it.