Why did you get her a harness??? This is not a good training tool! Get rid of the harness and get a good martingale collar. Click on this link. I just bought a bunch of these as they are great collars. My dogs wear them all the time and it's really easy to just clip on the lead and go for a walk. They are great as the dogs cant back out of them and they go loose when the dog is walking along with you. https://www.premier.com/store/Produc...x?cid=1&pid=11
Take her to Obedience classes. This way it gets her away from the house. Plus socializes her with other dogs and gets her leash trained.
Do you treat her when you get back to the house? If so, you are teaching her that she wants to go back home as she knows she is getting treats. She is training you well!
Take her for a ride in the car to the nearest park. Pick her up out of the car and take her to a spot where you can just stand or sit with her. She needs to be leash trained and this will give her a good start. Bring a toy with you, if she likes toys. Have her play with you with the toy. When she is ready she will want to start exploring. Then just follow her around. When she is more comfortable with you doing this, then you can gently start to guide her in the direction you want to go. Use the toy or food treats, whichever one she likes the best, when she is doing good. Don't treat or praise her when she resists. Just be patient and calm.
If she fights you and the leash just stand your ground till she stops. She will get bored with that after awhile and will start to walk around. If you give into her, she will end up being dominant over you.
If someone else is there with a dog that likes other dogs and puppies, your pup will start to follow the other dog. So walk her with other dogs! It's great to train her this way. Plus you can make good walking buddies and friends this way!
Good luck! Let us know how things go.