I have only read the first page - if it has moved on, I apologise.
I am 60 years old and when I was widowed, I 'inherited' an abused dog. We walked canals, forests and mountains. All very quiet places that I loved - and usually very safe. When he sadly died, I realised that HE had given me my independence to continue my life alone, so I got another one.
Perverts DO lurk - but not all day and every day. I don't see a bogey man behind every tree or bush, but I am an adult who can risk-assess in moments! Children can't because they are still learning the life skills.
DN (an only child whose Daddy had died) stayed with me almost every weekend. His Mum and I started to talk about transition to independence when he was 10 years old. We decided he was sensible enough at 10.5 years old (sensible is very child-dependent not age-dependent) and he was allowed to walk the dog alone with a mobile in his pocket. He was allowed to walk further and further as he showed us that he came back on time, contacted if he felt confused - or just wanted to phone in to say "A Okay". 
BUT..... he wasn't allowed to go to the canal or the forest without the dog, unless he had 2 additional friends. I was lucky that my own next door neighbour was going through the same independence challenge with her two boys of similar age. I took them to all the picnic areas along the canal and the forest first. We talked about non-safe areas (mud slides where they COULD come down too fast and into the canal or sharp protruding stumps). In essence, I taught them how to risk-assess.
Then they were packed up with a little ruck sack of drinks and food, a mobile phone and last-minute instructions.
I only recall one really bad incident in 3 years - the youngest of the 3 had gone into the deep grass to retrieve a ball and disturbed a wasp-nest and they were all being stung. The eldest child kept his voice calm enough to phone for help whilst he was wafting wasps away .... I was there in the car within 7 minutes!
So, I suggest that you run with your DD first, teach her how to risk assess for MANY eventualities and let her go alone when you believe she has learned enough skills and her 'in emergency' reaction. (That may only be a couple of weeks)