This is a tough question, and it's one that I had to deal with as the parent of a teen-aged daughter, too. My daughter Kayla had very severe asthma from about the age of 9. It was a constant struggle with her to get her to take her meds during her rebellious teen years. She would get very angry when she realized that she couldn't do something (like a stressful sport) because of her illness. Being a rebellious young lady, she would then lash out at me, and often seemed to blame her medical problems on Mom. We suspected her of doing some self-medicating (mostly alcohol) and some risky activities with the wrong kinds of friends. We purposefully sent her out of town to college, armed with information about how to manage her asthma, and she started to take more responsibility. Unfortunately, no one reminded her that some antibiotics have an effect on BC pills. So, while she was being treated for salmonella contracted from a turtle at the pet store where she worked, she was surprised to find that she got pregnant! (We still call Kyle our turtle boy).
Kyle was diagnosed with asthma at a very early age, so now Kayla is having to deal with it as a Mom. (What goes around, comes around!) She is now an expert on asthma and understands the drugs for it and their importance very well. She is extremely responsible about her own meds, as well as her son's. That's what it took for Kayla to come to terms with her medical issues.
I also saw two extremes while I was teaching. I had two young students who had diabetes. Kaitlin was the rebellious one. She tried to fit in with the other kids, would eat candy and junk food like crazy, and tried to deny that she had a problem. She would often wind up in the nurse's office with extremely high blood sugar levels. She also tried to "use" her condition. She would "mysteriously" have a blood sugar problem just before a test. She wound up being pulled out of public school and placed in a residential hospital-run school so that she could learn to manage her disease.
On the other hand, Ashley was one of the most mature young ladies I knew. She wore a monitor on her waist that would sound off if there was a problem with her blood sugar. She had no problem with explaining her situation to her teachers and classmates, and we all knew what to do if we heard the thing. However, Ashley took pride in NOT having the thing go off. She was diligent about her diet and her meds. Because of this, I had no qualms about taking her to an out-of-town convention. My husband and I and all of her friends who were in the van kept a close eye on her, and she had a great weekend. (Her mother was a bit shaky about it, but I kept in close contact with her). Since I've left the school, I've heard that Ashley is in the National Honor Society and has become the Queen of the Drama dept., starring in the yearly musical.
My point with all of these stories is that much depends upon the girl herself. You are lucky that your daughter is already past those awful years of 13-16. (I've survived 4 daughters going through those years). She also already has a passion for her softball, so I'm guessing that she is a very goal-oriented young lady. You can help her to learn how to manage her meds so that she feels the best that she can. After that, her own personality and sense of responsibility will have to take over. I know that depression is one of the side-effects of Lupus, and many of the folks on this forum deal with it. Luckily, I don't. You might want to subtly keep an eye on her for signs of it, especially if her disease is affecting her performance in her games. (The season is coming up, isn't it?) Otherwise, keep doing what I'm sure you are good at - being the cheering Mom on the sidelines and her best advocate.
I hope this helps,