And then the gf decides she wants to try a new flavor, buys her "normal" nic strength, and fills her vape up with it before anon has a chance to dilute it.
This would actually work out fine because she'd get he new bottle, hit it as hard as she did with her diluted bottles, then to proceed to throw up. The nausea alone from nicotine overdose should be a decent deterrent.
As someone who "quit" nicotine and picked it up again later multiple times... The first hit after a while felt amazing every time. Unfortunately. No nausea at all.
Nausea isn't overdose but that's a technicality, what I wanted to say is that it's quite hard to get to nausea off a single puff no matter the nic strength because it tastes, for lack of better term, sharp, very noticeably so. Coming off low-concentration juice you'd notice before the vapour goes past your tongue.