It really depends on the dog - some are chow hounds, some love toys. If she loves toys, use them as a reward. But I'd make sure not to squeak the toy when you are trying to get her to come - then you are using it as a signal and not the reward. If you are using it as a reward, then it makes noise after she's done what you want.
"Come" is generally the hardest thing to train with good reliability - one of the reasons a leash and/or good fence are necessary for good owners - because it's very easy for pups to find something more rewarding to do when they are already a distance away from you. If you think about it, when you are working sit or stay, you are right there in front of them (and usually holding something tasty). When you are calling her to come, she's a good ways away and can easily smell something more interesting while she's standing around.
At this stage, my advice is not to use the come command unless you can enforce it -- that means you shouldn't call her unless she's got a line attached and you can gently reel/coax her in. Giving her the option to refuse and being too far away to correct it means that you just made the word more meaningless. "Oh, I don't *have* to do anything when she says that..."