I am still new to Malifaux as well, (thaehl introduced me to this game not too long ago,) and I picked up Pandora as my starter. I am enjoying the manner in which she plays quite a bit! The way she operates is in preventing or hindering opponents from acting while causing them all to take gradual damage throughout.
Pandora is slow, so she is not suited for the impatient, and the little bits of damage that she deals would be disagreeable to players that like to see quick kills and instant results.
If your girlfriend prefers to slowly manipulate her opponents in gaming rather than striking with an outright assault, then Pandora is the way to go.
If not, though, she may consider looking elsewhere to start.