Most states require that a car has bee insured in the state it was registered. However, there are a few exceptions. You should check with your insurance company to find out their regulations on borrowing another person's car. Usually, the owner of the vehicle is responsible for the property, so there could be issues if there is an accident or other scenario.
If you will be driving the car longer than for a short visit, you should be added as an insured driver on her insurance policy for her specific vehicle.
There are too many variables to say whether your insurance will follow the car or the driver. The first thing you should do is check your insurance policy to see what exclusions it explains.
Make sure you are protected by getting an answer from your own insurance agent. Do not wait until your insurance is needed, such as the event of an accident or injury.