Each state and insurance company has their own rules and guidelines regarding auto insurance. Since you fiance is currently in college it is most likely the parent's insurance company has allowed her to stay on the policy because of still being considered a dependent. Once she is married to you that is no longer true and since she is living in a separate residence some insurance companies would not want to continue to insure her on the current policy.
Getting her onto your auto insurance policy will most likely depend on your car insurance company and their guidelines, if your fiance is not listed on the car's title as the owner. If she is, then you should be able to add her once you are married or residing in the same household. If her parents are the listed owners contact your insurance company to see what can be done. It might be possible to add her the way it is or perhaps her parents can make her a co-owner on the title. Check with your insurance agent to get an exact determination of how they can help you.
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