Hello Millar, just in case you are still thinking about the melatonin overdose threat, it doesn't kill you although check if her melatonin pills contain vitamin B6 as that can cause permanent nerve and brain damage. The whole bottle of vodka could be fatal as it can cause very low blood sugar and low body temperature, if your friend does overdose then the alcohol is the worst bit and it would be best to give them sugary things and blankets if they drink it. Hope she's fine now. I just made an account to post because I thought it might be useful from a science student's perspective, since most people usually just hear about liver damage from excessive alcohol. Just searched melatonin after taking 15, i knew it is taken in massive doses (500mg) in China but should have checked the vit b6, over 100-200mg can be toxic though only massive doses cause irreversible damage.
It may cause a headache and make you very sleepy

Bye