Neighbours keep jumping fence

Not happening to me but to my mum…. She lives in Gate Pa and the house behind her has frequent bouts of cracktivity. Theres been multiple instances of people jumping over her fence and using her driveway to get to the next street over. This morning she’s woken up and one of her huge shrubs has been snapped in half bc of someone jumping over her fence in the evening. Sometimes they throw their rubbish over the fence as well.

What can she do in this situation? The fence is already quite high and I don’t think she can afford to make it taller. She sent an email to a cops a couple months ago detailing the situation but was told unless there’s a face and a name to go off they can’t really do anything.