I had my doctor at that purple flower so often I figure she should at least be a m aster by now.But know matter how long she stays at the plants,she rarely gains anything.
I think it depends on the game.Or maybe even the computer. Because I have been on the game now for one week and my doctor isn't any closer to being a master than she was at the beginning.
She has healed many of the villagers but still her skill level never changes.