The policies you buy are only as good as the company who backs them. Combining policies with an excellent company is most always the smartest way to go. Discounts vary according to state insurance rules and regulations. There's no set discount across the board.
I just must give a response to the comment you had about the fact the insurance company didn't beat around the bush when your girlfriend had a claim. Contrary to popular belief, it's normally in the best interest of any insurance company to settle quickly on a clear cut claim. The faster they settle, the least likely the insured is going to argue about the settlement. I've never quite understand why consumers don't usually pick up on this. I hear it all the time, "they sure were fast" or "I had my check within two days". Just a word of caution: a quick settlement doesn't always equal a great company.
BTW, State Farm is the largest insurer of all property and casualty insurance in America. They are larger than Geico and Progressive, combined. Allstate is an excellent company and if you can qualify for them, USAA is also excellent. I would check with all of them before I went with Progressive. I spend a lot of time undoing and explaining problems that have occured toward insureds of other companies.
Owner of an insurance and financial services agency. Over 21 years experience.