Why would my sister's car insurance cost double that of mine?

Her 2 recent tickets. When I had 2 tickets on my record at 18 (I'm a girl too, but I have always paid by 6 month rather than per month, and my car is a 2001 mustang), my 6 month rate was around $1200. When the first ticket went off my record at 21, my 6 month rate dropped to $650 (over half of what it was with the 2 tickets!). By the next time I had to pay, my second ticket had gone off my record, and my rate was $450 for 6 months. I have 0 credit as far as I know, I've never had a credit card or bought anything on credit. I don't think your credit score affects rates too much. I did however pay for my car cash when I got it, so I've always owned it free and clear (which probably made my rates lower than someone who leases or is paying on a car). What they really care about is your driving record, which is the biggest indicator of your risk of getting in an accident. Your sister is lying if she says she took driving classes for both tickets, as you can only do that for a single ticket, once every 3 years. Her rate is something to do with that ticket.