Now, she sits before she lays down. I don't give her the treat when she sits, but when she lays down I do. I just say happily<"Good Girl Alex!" when she sits...Is that enough?
It really depends on what you want. My dog downs from a standing position. I didn't want to have the extra step of sitting first in there, eventually she will do agility and I don't want to add the extra time.
Are you using a clicker in your training?
If you want I can tell how to eliminate the sit before she downs.