Vicar, I can't offer advice, but it maybe it will help you to hear my experiences... :(
We have had similar experiences, except that mine have been 'up a level' because what started as in-school bullying developed over the years... My DS is now 17 and knows some very unsavoury people through school and in our local area. Also, he is (or has become) gobby and sometimes 'fights back', which probably doesn't help situations...
We have had eggs thrown at the house and bits of minor vandalism and criminal damage. But more seriously...
- We have had things stolen from the house, including 'minor' thefts such as alcohol taken by teens 'sneaking in', and a night-time burglary when our TV was stolen.
- I have had damage to my car, including 4 wing mirrors kicked off (in 4 separate incidents).
- DS has been beaten up and threatened. (Violence and fighting are very much part of the young male 'culture' round here, and sometimes DS has said he 'deserved' it for some fall-out or other... But violence is absolutely not part of my culture and it upsets and frightens me...)
- We have had online harassment in public forums.
- Just this week, we had a brick thrown through our window at night (when we were all in bed)...
Sometimes we have known exactly who was responsible. Sometimes, we have had strong suspicions. None of it has been 'random' crime, in the sense that it has always been targeted specifically at us (I think), though its motive generally seems pretty random - e.g. someone doesn't 'like' us (or DS). No-one has ever been successfully prosecuted for any of it.
I have felt huge upset, frustration, powerlessness and sometimes fear... Whatever I have done in each situation has not worked, and nothing has seemed like the 'right' thing to do, even with hindsight...
To start with, I used 'authority' (school or police) as my first response. I was slow to realise that this made me unpopular with parents and neighbours, who seemed to think most things should just be left to sort themselves out. Our first 'serious' incident outside school happened when DS was about 12, and was knocked unconscious by a 15 year old (for swearing at him)... But even the police seemed to think 'boys will be boys'.
DS was furious with me that I had involved the police and school, and even angrier when all the fuss (police interviews of him and other kids led to no official action) so after that, I let him make his own decisions when it came to harassment targeted specifically at him, but like you, I have made the decisions when it has been targeted at me or my house.
It is almost impossible to get 'anything evidential' (I shall remember that phrase). It is very hard to get fingerprints (forensics tried, after my burglary, and are trying again following this week's 'brick incident').
Talking to parents is very hit-and-miss IME. Most people don't seem to want to know, or look to excuse their kids, and on the few occasions I have done it, it has made me feel worse not better.
'Doing nothing' makes me feel like an idiot. And I think it led people - especially local lads - to think I was a soft target.
I can see why people 'take the law into their own hands'. I will not ever do that (because I am secretly an old hippy and believe "an eye for an eye makes the whole world blind"). But there is a cost to not retaliating. For instance, we know who threw the brick through our window (and he has stolen from us in the past too, and like your DD, he is someone who is a former friend), and DS really wants to get a group of friends together and 'get him'. I have asked him not to (not least because a broken window is better than a son in prison for ABH) and he has said he will not... But he is 'losing face' by doing nothing.
But the worst thing is, every time we 'do nothing' or the police fail to take successful action, I think it leads others (e.g. neighbours) to assume that we (well, DS) must have done something to 'deserve' it. People assume there is 'no smoke without fire'.
I understand why - when there is an incident, I also always ask DS if he has 'fallen out' with someone. Sometimes we can identify some spark - or we think we can - but in fact it makes me paranoid. On balance, I think DS is probably a pretty average teenage boy: mouthier than most, drinking and smoking more than he should but less than many of his peers, generally an OK lad, but having done one or two 'bad' things, and saving most of his worst behaviour for me... But sometimes I find myself wondering whether he's got up to things I don't know about, and all this is some kind of 'revenge'... The suspicion is really horrible.
FWIW, I think you are right to tell the girl involved what you think of her. IMO, a lot of teenage bad behaviour continues because teens don't think about the impact of their actions, and people rarely challenge them to make them think they just moan about them behind their backs.
I also think you are right to report each and every incident... But I wouldn't put any hope on that leading to anything much - you are a police officer, so you'll know how hard it can be to build a case.
If anything is said online, however, this is apparently easier to address. Take screenshots of everything you see. The police have advised me that it is possible to get a harassment notice after as few as two incidents of online harassment from the same person, so that would probably be worth considering...
Good luck with it. You certainly have my sympathy.