In theory it is possible for Wendy to draw like she did in the OQ, but she will need a regression therapist or psycho therapist, to bring her back to her earlier years. I think you become hypnotised and you mentally transform yourself back in time. I have seen script samples from those involved with it, showing how you wrote when you were 20, 12, 7, 5, and so forth. It certainly work. I think Wendy already have been involved in regression therapy since she already has talked about her earlier lives.
Wendy's art between 1978-83 is for me someone who express a kind of relationship with nature, a relationship which goes deeper than what's ordinary, or someone who express her feelings for nature which are stronger and more sensitive than normal, and I'm not sure if she really know the full value of those descriptions, or those emotions. I guess it was something she received more or less accidentally. I don't think that she has consciously chosen her style either, just followed the flow of time.
Another thing I have noticed is that Wendy change her style as the elves are gradually pushed away from their relationship with nature, or what I like to think as their rhythm of nature. The more the elves are attached to the palace, the drawing style become different.