Switchable batteries is a huge plus. You can go out, use up all of the battery. Is the battery dead? No worries, just plug in a new fully charged one!A Evic VTC mini or Kanger Subox would probably be great, they take batteries yes, but she can charge them through the mod if I remember correctly!
Then if she ends up wanting another mod or ends up getting into the "Let's swap batteries for a full charge" thing she can do that.
I'd probably show her and tell her about it, if she charges through the mod she might be inclined to roll with it and it increases the mods she could get by a lot.
Edit: A B&M with a juice bar would be great too, because she could test different juices and see what she likes!
Vapez