^^^
What they said, plus if your friend is on anti-depressants (especially SSRIs, eg Aropax, Zoloft, Prozac etc), chances are they'll block most, if not all, of the effect.
Years ago, I was on a lot of fluoxetine (prozac - ~60-80mg/day) and used to have to (well -
) regularly eat 4-6 blotters at once just to experience mild effects.
Having said that, though, I also remember taking 3 microdots (8() while on 'Serzone' (nefazodone?) - I dunno if that one's still around, but naive me expected the usual 'blocking' effects and instead (not surprisingly) had my ego blown to pieces for about 12 hours!
All in all, I wouldn't recommend a strong (from what I've read) trip for a first time for someone with 'mental issues', especially if medications are thrown into the mix... depending on their headspace at the time, it _may_ be ok to try out a small amount, wait 90 mins, check in, redose if necessary (and enjoying it) etc.. Ok, I'm sending very mixed messages here so I'll just shut up and let you/your friend decide.. have fun, whatever you end up doing!
[edit: one other thing - given that this is supposed to be about harm reduction, not harm encouragement [slaps self], one other piece of advice - to this day (I still have depression/anxiety issues), if I'm going to take acid I'll always make sure I have an 'emergency stop' drug of some form around incase things get out of hand. I've used chlorpromazine (Largactil, an antipsychotic) for this to good effect in the past, and even a big dose of Valium can prevent a trip to hospital.. IMO, antipsychotics work best to halt a trip, tho, so like I said, if she does go ahead with it, if at all possible try to have something on hand to put the brakes on if needed!]