Typically for this kind of offense, people get away with nothing, or a fine and/or a visit from CPS. I think it's cool that she got anything above and beyond that.
A woman in my city recently left her 4-year-old in the car, in the sun, on a very warm day. Kid was fine, but she was charged with felony child endangerment (or abuse?) because the child was left in the sun. The spokesperson said the charge would have been less had the car been parked in the shade, etc. Cops and judges do have some discretion in how to enforce/punish in these cases.
I also wouldn't be surprised if PPD played a role (not because of her age or anything, but because of the reports that she seemed emotionless). Our fire department called me out once to check the seat of a woman who left her newborn (2 weeks old, I think) in the car while she went grocery shopping. The mom was COMPLETELY expressionless despite the firefighters and police all over the place, despite the fact that she got a ticket and a report with CPS, despite all that. Completely stoic. Not making excuses or acting like it was no big deal, just acting like nothing was even happening.
I felt so bad for her. Angry, yes, but my heart was breaking for her because I just felt like there was something more going on. I wouldn't have wanted that woman to lose her license or go to jail. I wanted her to get some help, which hopefully she did through CPS.