As to how you address your friend on this issue, it seems to me to depend on just what these pills turn out to be. It's one thing if she's trying to placebo effect you with vitamin C, and quite another if she's sent you PCP or something hideous. See what I mean? Either way, she screwed up, but friends do that with eachother all the time, screw up in some well intentioned way. And factoring in mental illness, and you only get more liklihood of such goofs.

Once you know what the pills are, you will probably have a better idea what it is you want to say to her.

Nice to know you're alert enough not to take the pills. Good for you. Also your friend seems lucky to me that you didn't just mow her down with a knee jerk emotional reaction. Good job. Smart. Compassionate, even in the midst of your own pain and confusion. Good qualities all.