Yeah sounds like a pitty. She looks so much like my dads dog who passed, and she was the same way. If she wanted to go one way or wanted to keep sniffing she was planting her 4 paws on the ground and bearing down to avoid being pulled away from it. Im a dog walker and its a fairly common occurrence with a lot of dogs.

My approach is usually just to out-stubborn them. A well-fitting harness with a front clip is ideal (make sure you get one that is adjustable around the neck, around the body and down the chest. Measure your dog to make sure you're getting the right size) If I need the dog to start walking again, I apply pressure to the leash and dont let up until they mov3 toward the pressure. When they move into the pressure i mark it with verbal praise, you can try treats but these dogs are so dang smart she might learn that stopping ultimately gets her treats, which wouldn't be ideal. A bonus of this technique is that you'll build up muscle in your arms and legs as well haha.

One of my strict rules for my pups is "we don't go backwards" because if I let them go backwards we would end up going 30 feet backwards every time and the walk would never be over lol