Don't feed charlatans and fraudulent preyers on the vulnerable, bereaved or gullible.
I would imagine that if your friend is tempted to visit a medium, she's bereaved, vulnerable or in some way at a low point, so there will be other, better ways of addressing this.
I have never for a moment believed in this kind of nonsense, but it's telling that the one time I went to a medium (persuaded by my sisters), over 20 years ago, I was a couple of months in recovery after an accident, still visibly disabled, poorly-dressed, unemployed, with no firm future plans, and had had to move back in with my parents.
I think I thought that if she predicted nice nonsense, at least I'd have that as a comfort while I tried to figure out my future -- which shows you how vulnerable I really was.
The funny thing is that she did predict what she clearly thought was a lovely future, based on the nonentity in front of her (I was going to 'settle down' locally, move in with my boyfriend and have a daughter within the year and open my own 'little business, selling things on the internet'), but in fact, despite not presenting to her mind as anyone ambitious or go-getting, within a few months I'd won a major international scholarship for postgraduate study abroad at an elite university, did two further degrees, and lived a fulfilling, career-focused life in other countries, and only had a baby (a son) fifteen years after the 'prediction'. 
I remember specifically asking her if I would ever study again, or if I would ever live abroad again, and the answer was an emphatic no in both cases. I imagine because, for her, emigrating was a sign of poverty, and studying was only something you did if you didn't have a job...