Are there any other SONOS components in the house?

Yes all mine a play one in kitchen 

Find a place of your own? 

Why would she do that? Do you play the system too loud or at time that do not fit with her? My first reaction would be a good conversation is in order, but you seem to be past that point. Access to Sonos is open for all people that have access to your wifi. So that is the point to start. Change the SSID of the network. If she has access to the router she can easily rectify this though, and it would not be very nice to stop all her internet access.

So might be to use the current SSID and password on a travel router that you’d put on your network and use the main router for your own network - this way she would have access to the internet, would not have to change SSID and password and might not even notice something’s changed. She would however not have access to the Sonos devices. Again, having physical access to the main router would mean she could change things.

You should be able to change the password on your Sonos account.  Your ex would still be able to connect to the system but not do system management tasks (like deleting your system).

Thank you guys very helpful actioned the messages