The girl is committing a crime of trespass. She has to learn that she may NOT go anywhere she pleases to go.
If SHE is allowed to continue, the next thing you know (as happened to us), more than the one inconsiderate girl (or boy) will be cutting through the property, maybe they will (as happened to us) choose to SMOKE on the property, or VANDALIZE the property. OR worse case scenario, if injured while trespassing, SUE the owner for damages. A sleazy lawyer can convince a judge that the property was an “attractive nusiance,” like a trampoline that is not enclosed, but nonetheless accessible to kids. There are crazy people who will actually BUY that notion and give the homeowner grief.
You cannot set a precedent by allowing this to continue, UNLESS you want it to. Next time this happens, follow her into the school and report her directly. The police will probably not do anything for you.
If this were one of our yeshivah kids, it is still a problem, and they need to learn derech eretz. No one should cut across someone’s property without rishus (And if they needed access, I probably WOULD give rishus, but do not assume that to be the case without asking). I taught my kids that from day one.
I have to constantly tell frum little kids to get down off my retaining wall. The problem is sometimes their parents are WITH them, watching them do it. I come out (yes, I am that old lady on the block I swore I would never be) and tell the parents that NO one is allowed to climb on the retaining wall, it is not safe, and it is private property, so get your kids down. Some of them even say sorry. Most do not. And THAT is what’s wrong with this generation, in a nutshell. How can kids learn derech eretz when their parents don’t recognize what that means?