Ok, so don't think I'm trying to defend this lady (she's all kinds of wrong for even making that type of statement to anyone), but it seems she's probably just having a hard time adjusting to her surroundings and being older than everyone else. As a non-traditional student myself, 27 years old (got one semester left, wahoo!), I was constantly comparing myself to the younger crowd (practically everyone during my first semester) and how they could almost....consume....information. This was going on while I was medicated too, so this is most likely a normal response. The fact that you're already in the program suggests that ya'll are at least Sophomores, right?

How to deal with the situation depends on your temperament:

Myself, being a moderate-tempered techno-redneck, I'd calmly convey to her that she, as a future nurse, should better understand the point of this medication. That you (just like Maus5321 and I) are not medicating for a competitive edge, but to achieve a normal level of cognitive focus and motivation. So go to Hell. (last statement optional )

Another of many alternatives would be to report her for harassment, if she keeps bringing it up. Universities take learning disabilities pretty seriously and will take some sort of disciplinary action. You are paying for your education, so your learning should not be hindered by some lady quacking at you for being unique. But then again, theres the thought that you'll be in the program with her for a while, etc.....My garsh this can get convoluted

Not sure if your school offers it, but maybe she should look into non-traditional study support. (We gots a whole center.....go KSU Owls!!, lulz)