I owned a life insurance policy on my sister and made the monthly payments and I was the beneficiary

My parents had life insurance on me and my siblings when they passed away I became the owner and payer of the policies My sister pasted away recently now my niece her only daughter wants the life insurance money. I paid for the funeral and want to buy the headstone my niece has been calling me daily saying she has the right to the money that will be left over even though she never helped pay for the policy for the last 12 years. Everyone knew about the policy and I asked them to help pay for them and we would share equally but they wouldn't help