You can try pulling it. Use a slow steady traction. Don't yank or pull too hard it will break off. If she is still open you can insert a couple uterine boluses made for cows. They help break the retained afterbirth down and fight infection. If you can't get your hand in there you can't use them.
Definitely highlighting not tugging on it. The rag is a great way to add some weight to it to slowly pull it out, and you've already given her some oxy to cause some uterine contractions to expel it. Breaking the placenta and causing a bit to become retained is one risk factor that can occur with tugging. It can also cause a uterine tear or invert the uterus, possible even cause a prolapse. If she had a lot of kids and/or very big kids, it can be hard for the uterus to contract down after a birth. Not sure if a goat uterus has a fundus to palpate like in humans, hah!
Adding a little more weight might assist with the expulsion.