It depends on your child and the risks in your immediate environment. I live in a rural area where all the children and parents know each other and where traffic is minimal, so my DS8 has been playing out, with increasing levels of independence over time, since he was 5 or 6. We're at the point now where he is allowed to play out and explore within a boundary area, he is allowed to take his bike or scooter, and he is allowed to knock for friends. He is not allowed to play at friends' houses without asking first, he is not allowed to go outside his boundaries, he must wear his helmet at all times on the bike/scooter, and he must come home at the exact, agreed time. Any violation of these rules means he is not allowed to play out the following weekend. On the whole, the free-range experience for him is very positive and he mostly adheres to the rules. He doesn't think it's worth being under house arrest if he breaks them.
Perhaps start with some short play periods, with defined rules and the responsibility to return home at a certain time? Have a talk and explain to her that if she is able to follow your rules, you will trust her more, and she is likely to get more responsibility. Also explain the consequences of her not following your rules (whatever you decide they might be) and enforce them if she doesn't comply. Is also having a chat about stranger danger. We talked very clearly about it not being OK to walk away from friends with an adult - even if they promise you sweets, and even if they want to show you their dog, their new video game, or anything else.
The other best investment for my peace of mind was a walkie-talkie set. We don't chat to each other, but if he gets hurt or ever feels intimidated or out of his depth, he pushes that red button and I can find him, and help without it being obvious or embarrassing for him.
Mind you, this is just how we do things :) I hope your daughter loves her new freedoms and is able to manage the responsibility in a way that keeps you sane and worry-free.