Even though you may be with your sister, your roadside assistance only covers the vehicles that are listed on your policy. The price you pay for roadside assistance is built into your policy’s premium, so the coverage isn’t able to extend past the insured vehicles.
If you’re looking for broader coverage, a general roadside assistance program apart from your insurance may be better for you. Services like AAA or National General Motor Club allow you to add additional family members and vehicles.
You may be able to save money in the long run with a separate membership, but you’ll need to compare pricing to be sure.”