Sounds like it's quite undercharged: dangerous driving and causing serious injury (charges usually laid for a reckless accident not an intentional act), and causing harm to a Commonwealth public official (which could be laid for relatively minor injuries).

Either they know something we don't, or they're going soft on him for some reason. Why not attempted murder for example, if the intent was there? Perhaps he convinced them somehow he genuinely didn't want to kill and only intended for her injuries to be minor, perhaps her political leanings were not to the police's satisfaction to go hard on the charges (or maybe there is more coming). Maybe it's a deal to plead guilty to those charges rather than fight more serious ones on the grounds of insanity.