@Rosemarie111  There is a flag symbol next to the guest's message. Click on that and report the profile as harrassing you. Also call Airbnb, tell them what's happening, tell them to look at her messages, and to block her from contacting you again.
 
P.S. You don't need to decline or preapprove Inquiries. Just messaging back once within 24 hours fulfills your obligations.