You could make it more simple.
While under the effects of neurotoxin, for ~1.5 seconds, you don't see your hit points drop at all, and when neurotoxin wears off, you see your hp drop as though one ability did all that damage.
Smart players would pay more attention to which ability it was that was preventing them from seeing their hp drop, and would back off after that extremely dangerous skill. It would mean avoiding that neurotoxin is more important because it screws up the information you normally get.
You'd want it to have a very distinct visual cue though. Perhaps a purplish multicolored aura around you to signify that you're under the influence of dangerous toxins.
Even high level players would have a rough time gauging how many hp they actually have when they get hit by that. It would add a new level of counterplay to fighting against her, because you'd have to start remembering how hard each player is hitting. her late game utility in teamfights would be incredible because she'd be extremely effective at either: a) poking out a target and making it retreat, or b) making a target overconfident and getting them killed.
Voice chat and communication between players would be capable of defeating the effectiveness of it, so its duration can't be too long.