Pictures can lie(make things seem bigger), but from the looks of it she looks to be over 100 grams. I'd say she's most likely had at least 3 meals but I just don't like his excuses that he gave you when you inquired about the snake you were interested in. As far as her being nippy, that's why I said to hold them for a bit to let them warm up. They sometimes as babies won't strike if they're cold, but once they warm up like she did in the car you got a picture of her temperament(possibly). Though it may of just been briefly or she may be nippy for awhile and you'll have to work with her to get that out of her system.
I would say to try rat pups as well since he thinks that's what she's on. I mean judging by the picture size that's what I would have her on as well. The reason he did pre-killed is because the rat pups can bite, so if you choose to feed live just monitor her eating to make sure she gets a solid bite/coil and doesn't end up getting bit. I would try frozen thawed if it were me and all of my snakes eat frozen thawed because I find it works best for me, plus I don't raise my own rodents. If you have any questions feel free to message me or post a thread, whichever is easier.