Due to agreements with the patent holder, Cephalon, that were made in 2005-2006 several generics manufacturers are now allowed to sell generic Modafinil. I have found confirmation that the manufacturer Teva has begun selling generic Modafinil, though I haven't seen news about other manufacturers. However, the article also, says that Cephalon is a subsidiary of Teva, so perhaps this won't have an effect? The Modafinil patent is set to expire in April 2015.
Let p = the probability of the drugs being counterfeit. For what values of p would you be willing to buy the drug?
Her price isn't that great, even with the Reddit discount, so I'd say something like p>0.2 would be enough to push me to buy from the Silk Road or one of the other online pharmacies instead.