Dr Poison has what it takes to be that rarity in comic: a genuinely scary villain. First of all her dedication to the experiment above all has some nasty callbacks to some genuine real-life cases, such as http://en.wikipedia.org/wiki/Graham_Young

Secondly, the fixed grin and wide-open eyes could potentially be even more disturbing than the Joker's. When the Joker smiles it's largely voluntary (this can vary, but for the most part), but with Dr Poison, she's going to have the same expression no matter what. If you play up the drooling a little it emphasises the sheer inhumanity of the character.