I used to give my dog a Kong with wet dog food in it. Throw it in the freezer overnight, give it to her in her crate in the morning before you go out. Much safer than rawhide (they can cause all sorts of medical issues with some dogs) and it should keep her entertained for a fair amount of time.
Editing this to add something about deer antlers, which were suggested. Last year I had given my two dogs deer antlers to chew on while I was at work, and one day when I came home I found some small shards of the antler on the floor. I thought it might have been a fluke, so did buy them deer antlers again a few months later, this time keeping an eye on the dogs as they had them. And again, one of the antlers began to splinter into sharp little shards once it was chewed down. I no longer consider them safe and would not recommend them.