What damages were done? Are you accusing her of theft? Is their a dangerous condition that might injure her? The minhag of children is to take short cuts.
To put “tresspass” into context, until about 250 years ago, you had alledge (even if they ignored it most of the time) that the tresspasser had come into your property with force and arms and against the king’s peace – schoolgirls taking shortcuts didn’t count.