Best case scenario he'll get second degree. Even if it had been an intruder, he unlawfully opened fire with an intent to kill while his life was not in danger.
Personally, I'm certain he intentionally killed her. His whole story of, "I didn't have my legs so I felt scared like a little babby girl." is utter bullshit. He's a grown man, not every bump in the night is a boogy-man trying to kill you.