Anti-Social Neighbour Problem & Trespass?

thegreenone

I'm sorry your friend is going through this.  I have no idea how to go through official channels other than those suggested ie keeping a log.  We borrowed a Blink system years ago but this needed WiFi and went to the owners phone.  May be helpful, maybe not.

Okay, odd one.  Years ago we had a problem with cats going through our garden.  It was a Feline Highway which resulted in 'mess' and cat fights.  We bought some cat repellents.  They did nothing for the cats but our sons could hear them and wouldn't go out in the garden until we got rid.  It was something like this.  Pilmoux Cat Scarers for Gardens Cat Repellent Ultrasonic Fox Deterrents Animal Repeller Battery Powered Waterproof Motion Activated Sensor for Bird Squirrel Dog Pest Farm etc : Amazon.co.uk: Garden  It was 20 years ago.
Just an inexpensive interim thought.

Drawingaline

Definitely see if you can fence off the right of way passage from the rest of the garden to ensure that your friend has the privacy of her garden, but the accessway is still accessible the neighbours (as this is something that is required if it is written inyo the deeds) Maybe invest in some earplugs or even headphones and basic music player to wear when they are out in their garden so they can ignore the noise and swearing from next door. Maybe collect anything thrown over the fence up once a week and just stick on the doorstep of next door. (As by fencing off the right of way access they can no longer get into the garden) 

Cameras seem a sensible suggestion and if it would give them a little more peace of mind might be worth it.