The thing is, things are NOT NOT NOT more dangerous now than they were when we were kids. Your kid has a .00001% chance of getting swiped.
I believe in safety in numbers, being aware of your surroundings, and preventative education. Don't go help that guy in the van that you don't know find his puppy. If someone starts driving slowly past you, get away. If someone gets hurt, know what to do... etc, etc, etc.
I would start slowly; let her and her friends walk by themselves, and you leave 10 minutes after they do. While you're there, read a book, don't hound the kids (stop pushing, slow down, etc).
Then increase the time; leave 30 minutes after she does. Never let her go alone.
Then start leaving before her; make sure she has a watch, knows how to tell time, and when you expect her to be home (and not one minute later!)
The only way we're ever going to teach our kids independence and self confidence is if we cut the umbilical cord!! I say go for it, and GOOD FOR YOU for taking baby steps towards this!!
My kids are 6 and 8, and I let them ride their bikes down the street to the stop sign (just out of eye sight) and back; they have never once had a problem, and have never once let me down. You know your kiddo better than anyone else, it's up to YOU to start trusting her and guiding her!! :)