Dont worry about it
That is your human side talking
People all too easily see stories about tragic events and very easily turn the page
You are reconnecting with your human emotional side and there is nothing to feel ashamed about
Perhaps this girl could have been a sister, cousin, a friend... just putting her in that context has shown you how vulnerable we are
Talk to someone close to you and if they say you are being silly they are being very insensitive
Believe me the guy who caused the accident is probably getting grief from more people than you know
Edit: Sorry just saw the bit about your brother. My condolences to you and your family even though it happened awhile ago
My flatmate lost his brother in a hit and run. I have only been living with him for 7 months but I know he has flashes where he suddenly gets angry/irritable or very down. I know his other brother still hasnt gotten over it
My advice would be to speak to someone about your feelings. You need to let it out