If your daughter has face-to-face classes (or even if she doesn't, actually), take a look at the
HOPS program for teaching executive skills. It is research-backed, and designed to teach kids in middle school who have troubles in this area. It is somewhat expensive, but I was able to get a copy through interlibrary loan to "try before I buy." It is a very structured, week-by-week plan that doesn't try to do everything at once, and is designed to fit with teachers' and administrators' busy schedules. Even if it needs to be modified to fit your online school model, having a starting place to modify from sounds like it would be useful.
Good luck.