Have you ever been in an accident?  She could have been in shock and didn't think about what to do.  She might not own a cell phone, not everyone does.  At least she called 911 when she got home and reported the accident.  I'm sure the police investigation will work through all of the questions you have and will assess the correct remedies for her actions following the accident.
As for the baby out at 1:55am, who knows?  Maybe she was coming home from work, a family member's house, a friend's house, it really doesn't matter what she was doing out with her baby at 1:55am.  

Now, let's hope for the injured man gains a full recovery from his injuries.