A top performer misses a lot of work. What is the best approach?

Since 2009, I have been supervising a small team that is considered highly effective,producing notable results, especially in the last year. One team member in particular stands out. She takes a somewhat leadership role in many of the team projects (although she explicitly states that she has no desire to lead a team as a supervisor herself), comes up with many of the ideas we implement, and will often drive completion of various goals. This she does while completing daily tasks quite efficiently. Unfortunately, she has always had a high rate of absenteeism (even before I became supervisor). She suffers from asthma and respiratory illnesses, sometimes coming down with pneumonia. She feels really bad about her attendance and has consulted her doctor, working on different treatment plans to get her illnesses under control. When I consider what she contributes to the team, I will often overlook many of the absences, making sure that the rest of the team is ok with their workload, gaging how they can be helped to not be overloaded due to her absences. For the most part, she is able to catch up without needing extra assistance and the others are very understanding. However, I am wondering if there is something more I should have been doing. We have new members in the team as I will be leaving on maternity leave soon and already I am noting some discontent from the new members due to the amount of sick time this top performer has been taking. What is the best thing for me to do here?