Congratulations for nursing this long! You are obviously dedicated to providing the best for her. Are you sure that you need to wean to be treated? I agree that you should call a LLL Leader or a Laction Consultant right away. Have ready the name of the medication(s) your doctor wants you to take, and if you have it, any other possible meds that could be used. They have resources that will help you make an informed decision about if the med is compatible with breastfeeding. Remember, you can take a lot of things now that you couldn't when she was a baby. She's taking in less breastmilk, and she's big enough to process things she couldn't before.
Having said all that, if you decide to wean, the best way to do it is gently and with love. Most people recommend cutting out one nursing session at a time. After a few weeks, when she's had time to get used to that, cut out one more. Start with the one she's least attached to. Do you think that your DH could put her to sleep? That could help you cut out that one. Additionally, your DH could sleep with her and you could sleep in another room for a while to try to cut out night nursing. As for the first morning nursing, I'd try to have something there to distract her as she wakes up. You might want to try getting right out of bed, having fun foods for breakfast (that you prepared the night before so that it doesn't take much time), or just some snuggling and a story.
Good luck!