Most insurance companies require anyone above driving age (16, usually) to either be added to the policy as a driver, excluded, to added to the policy as a non-driver. In this case, she will most likely be an excluded driver, meaning she isn't allowed to use the vehicle.
Short term insurance is available in Michigan but you would have to contact a local agent in your area for assistance. LA insurance is the most common issuer of weekly policies in Michigan.
They would only need to be listed as drivers if they live in your household and/or drive the truck on a "regular" basis. Most companies consider "regular" use as 12 times or more per year.
If you are married then there shouldn't be any issue with you insuring the vehicle. If the registration is also in her name then she will need to be listed on the policy.
Coverage & Claims
Page 58 of our State of Car Insurance Report shows that an accident in California has an average impact of an additional $899 in premium per year. These numbers are averages and there are other factors at play, but that should provide a ballpark figure as to what you can expect.