rent property sale

I own a duplex in Upstate NY. I live in one side and rent the other. I put the property up for sale last month. My problem is, the agent can never get in to see the rental side because the tenant is never there when she shows up. The agent calls her with 24 hrs in advance, but she never picks up the phone and claims she never got the message on her machine. When she is there she claims she is too busy to show. What are my rights as a seller? If I give the tenant 24 hrs notice can I just go in and show the property? The tenant told me she will call the police if I go in and it is not an emergency. Do I have any legal recourse because she is hindering the sale of my property. If anyone can give me advice, please let me know. Thanks
She is on a month to month basis, with no lease.

Rent Back Fast