Based on what you state as your girlfriend's needs and preferences, the good old
510 battery (with 510 cartomizers) might be very good for her.
And, yes, do include a
PCC for charging one battery while vaping the other (and for carrying cartomizers).*
Cignot and
LiteCigUSA are among the lowest cost suppliers of Joye 510 starter kits.
LiteCigUSA has the better price on the PCC. [FYI:
MadVapes has a very good price on a
Bauway (i.e., not Joye) 510 PCC kit (with a different style PCC).]
For heavy vapers (like most of us posting in this thread), those 180 mAh batts would be frustrating (scratch that;
were frustrating: that's what we were vaping last year

), but they may be fine for your light-smoking girlfriend. And indeed stick with the
regular resistance 510 cartomizers.
* [NOTE: I'm not sure how well cartomizers fit in the traditional 510 PCC. FYI: Volcanoecigs sells this
Kr8-style PCC fitted for their Magma 510. It might do the trick.]
BTW, seeing that PCC reminds me that there is
another model she might also want to consider: the
Kr8, which has a
280 mAh battery and a
huge selection of prefilled cartos. I describe it (and list/link suppliers to purchase it from) in
this article. Of course, the two of you could not share cartos with this one.