Regardless of "legal age", and with an understanding of your daughter's age and how mature she or you think she is, anything can happen. I would at least have a trusted neighbor or someone check on her every now and again.
When I was a child, I lived in the country in a small town where no other houses could be seen, but our home was robbed two times. Anything can happen anywhere.
These days with all the stories you hear on the news about teachers, ice cream truck drivers and "regular" people molesting, raping and abducting children, that is not a risk I would take. And just to be extra cautious, you should get on line to check if there are any registered sex offenders in your neighborhood.
The fact that my house was in the country, shows you that somebody was watching to see when my family was home or gone for the day. You never know who might notice these things. For the sake of your daughter, please be careful with your decision. I know my baby is the most precious gift to me, and, unfortunately, no one can be too careful these days.
Please take my thoughts into consideration.