Couple questions...

I'm new to crystals and I was wondering what crystals and gemstones would be good for a friend diagnosed with bipolar 2 disorder, borderline personality disorder, and hallucinations. I'm planning on making her a crystal/gemstone necklace or bracelet for christmas.

I've only heard of one crystal, lithium quartz, but I was wondering if it would interfere with lithium medication? Her lithium dose was lowered because the normal dose made things even worse.

Lovely Idea RavenHart and I think lithium quartz, black tourmaline and selenite can help.. maybe a mix of the three? I wonder what others might suggest. A dear friend of mine said he would not be without black Tourmaline and his illnesses sound very similar to those you have listed.
blessings
Marina

Lepidolite is very calming and balancing and contains lithium. According to "The Crystal Bible" by Judy Hall it is good for Bi-polar disorders.

I think you have a great idea there for your friend!

nerves

amethist seems good for nerves...
being bi-polar, I guess your friend needs also a strong nervous system...