I've never heard of someone being poisoned by touching a napkin. Is there some substance that can be absorbed through the skin so quickly? Sounds like something in a murder mystery or sci-fi story.
If she tasted garlic, it was likely involved.
https://www.webmd.com/vitamins-and-supplements/dmso-uses-and...
In this case, I'd guess that what was on the napkin is "nothing", and her mind does the rest of the work. Though tingling in the fingertips can be produced by a vast array of substances, and my second guess would be "napkin smeared with Ben Gay".
Dymethylmercury immediately that pops into my mind