There is no doubt in my mind that your pup should be in the crate while you are gone. It is far more safe and she will also feel much more safe while you are gone. A big back yard is way too much for a young pup to guard for that amount of time.
Oh, by the way, welcome to GRF. Be sure to post some pictures of your pup.
Oh, by the way, welcome to GRF. Be sure to post some pictures of your pup.