Hi, I'm Dr. Bonk. I'm sorry to hear about Emma's troubles. Large breed dogs often develop issues with their hips that make it hard for them to get up, but once they are up are usually fine. The issues can range from hip dysplasia, to arthritis, to muscle weakness. With any of these there may be inflammation present that mainly affects her while she is pushing to get up. Something you can try is to start her on a glucosamine supplement. There are a variety of pet options available. Glucosamine has to build up in the system, so it will take 1-2 months to reach the full affect.
In the meantime, you can give an antiinflammatory. Aspirin works in a pinch, but it is best to get her on a safer alternative like Rimadyl, Previcox or Metacam. You can try aspirin for a few days to see if it makes any difference. The dose is 325mg per 30lb body weight, given every 12 hours, best with a meal.
Finally, exercise is good for both arthritis and muscle weakness. Walking is good, and if the antiinflammatories get her to feeling better, sit-to-stand exercises or walking on an incline will help strengthen those hind leg muscles.
I hope this helps. If you have any other questions, please let me know. Thank you and good luck!