If you will be driving the car, you need to add her to the policy. This will avoid the insurance company having any reason to deny a claim in the event of an accident.
Car insurance is incredibly specific - it can change based on your zip code and the VIN of your vehicle. So, it's going to be near impossible for me to give the company or car that will be the cheapest.
Coverage & Claims
You might be a good contender for this policy option. Most lease contracts will require you to keep the vehicle in good condition.
If your sister lives with you or uses your vehicle regularly, she can be added to your policy. Given her age and lack of driving experience, I would prepare for a big increase in your premium.
Car Insurance Costs
You should never have to pay for a car insurance quote. Since auto insurance is so specific to each person, it would be impossible for companies to advertise a set price to take out a policy.
The maximum allowable number of drivers and vehicles that can be insured on any particular car insurance policy will vary by company. While there is no set standard, most insurance companies will allow their customers to insure up to 4 drivers and 4 vehicles on a single policy. This does not mean that you cannot insure more drivers and/or vehicles with your car insurance company if that becomes necessary.
Coverage & Claims
A car accident can have a fairly significant impact on your rates so if they damage is not extensive, as you say, you might want to consider paying for the damage out of pocket. Ultimately, that decision is up to you, but our State of Insurance Report (page 58) shows that at fault accidents in North Carolina will cause an average rate increase of $426 per year to your policy.