No, this would not normally be possible for a few reasons.

One is that likely your insurance company would not allow you to insure an out of state vehicle that is not garaged at your home, not driven by a member of your household and not registered in Pennsylvania. If you did not give your insurance company the information that it was your sister's car registered, driven and garaged in New York when adding the car, nor have your sister listed as a driver on your policy then this could be determined to be misrepresentation, a form of insurance fraud.

A second reason that you cannot insure your sister's NYS registered vehicle with PA auto insurance is that New York laws require vehicles to be insured with NYS insurance.

The NYS DMV states that the liability coverage must be NYS insurance coverage, issued by a company authorized to do business in NYS and licensed by the NYS Insurance Department. Out-of-state insurance coverage of any type is NEVER acceptable or valid. Again, if your vehicle is registered in NYS, the liability insurance coverage must be NYS insurance coverage, so your sister getting a PA policy would not be accepted according to New York laws.

Your sister can get car insurance quotes for New York State, by simply clicking here.