Despite her faultless logic, emotionally she's likely to be two thirds of her chronological age so experiencing altered states of consciousness at 16 isn't a great idea IMO.
Both are illegal at her age, if she's a rule-follower.
The alcohol she couldn't legally buy in a shop, so you could tell her she can try it when she can legally buy it. That gives you a 2 year leeway as shops are really hot on ID for youngsters buying alcohol.
Where is she going to buy the Ecstasy or other pills she's interested in? Because wherever she'd get it from, both she and the seller are doing something illegal.
How would she know it's the real stuff and not something made in someone's kitchen with drain-cleaner? It's not as if the suppliers have a Customer Services section, or pages on Revoo is it?
I'd be concerned as to where she's got the idea she needs to build resilience to different substances because it's a bizarre.
People in Rome or the Middle Ages (at least in some novels) used to do this sort of thing if they were royalty or politically active targets for being poisoned by their power-hungry enemies.
If she's thinking ahead to maybe her drinks being spiked in a social setting, that's usually done with date-rape drugs like rohypnol, not a common street-drug.
Get clued-up yourself on all the modern trends and terminology and find out how addictive or not some things can be. www.talktofrank.com/
Explain that the 'what goes up must come down' philosophy also applies to drink and drugs. Everybody will tell her about the nice effects, not many will talk about the comedowns, the shakes, the paranoia, the irrational fear and panic attacks.
Also explain that as her brain's wired differently, she may experience the effects of drink and drugs very differently to an NT peer.
I'm not for a moment advocating this approach, but in my generation, if parents found you'd been drinking, they gave you enough alcohol to make you throw up several times and have an almighty hangover and splitting headache the next day, that cured a lot of kids from wanting to over-indulge.
Cigarette smoking, my friend's Dad made her brother chain-smoke 20 cigs even when he'd started to be sick, he grew up to be a non-smoker.
Hope some of that helps, 