Short answer-- maybe the Mi-one (it's tiny) or the Tarot nano. The nano is the smallest thing I own. Coils that come with the tank are 0.5 at the lowest, however, so I don't know if they would be too much "med" per puff.
Her liquid needs to be in traditional, vapable form to use a regular eliquid device and many of those liquids just come with pretty much a cheap, rebranded ego pen type vape. So you should be fine with your run of the mill vape stuff.
I do not recommend COMBINING it with ah, nicotine eliquid, that can tend to make a person cough, so I am assuming this is just for her medicine so to speak but if she's vaping nicotine also, I kind of would recommend a separate device.
If the liquid is oil or wax based in any way, you are going to need an entirely different type of atomizer, and you'd be better off asking this question in a forum oriented specifically towards those types of vaporizers.
Good luck,
Anan