"She turned pro but is too young to join the LPGA so she is a pro golfer without a tour. "
This is not really correct. The LPGA does have an age limit of 18 but you can file for an exception like Morgan Pressel and Ari Song did. Wie did not do that.
Why she chose not to file, I don't know but with $10,000,000 from Nike and Sony and appearance fees from some of the men's events that are greater than the total purse for the event, I assume she's not in any hurry.