I went through this with 3 dogs. I penned the dog, Trip, and only let him out when supervised. Not all dogs, but some hit this stupid teenager stage and they want to play with the lambs, sometimes the ewes. I would put Trip in the barn and let the sheep out in the pasture, then vice-versa. If we left, I made sure Trip was penned where he couldn't chase the lambs. He got lots of supervised "visits". He finally outgrew it and is now perfectly safe with all the sheep.
I had another pup, Sentry, and he started chasing the lambs. I put him with the weaned lambs, but he chased and played with them. I penned them at night and when we left, with him in a lot next to them. It took time and training. I let him with the lambs under supervision, praised him when he was good. I would make the lambs run, just to excite Sentry into chasing, then I lowered the boom on him. A rolled up paper feed sack makes a wonderful punishment. I beat the ground, the fence, my leg and him with it. It was terrifying to him. I also yelled, scolded and made a lot of noise. Then I penned him for punishment. He finally outgrew it. He now is my "lamb" guard and is in the barn at night, even when the ewes are lambing. He respects the ewes, gives them space and doesn't mess with the lambs.
You have to take the dog out of where the lambs are for their safety and so this doesn't become further ingrained in the dog as a behavior that you do not want. Cowpanels and T-posts make great easy and fast pens. Cut one in half for a gate. You can put them together with hog rings or hay string. The pen will have to have shelter, shade from the heat and a cover for rain. You want her to be with the lambs, by proximity, but only out with them when you can supervise.