This is kind of a "tinfoil hat" theory, but....... how did Wayforward get the time to work on Jammies mode? Think about it. While they already had a base for her in her pajamas from the opening of the game, they still had to create new animations which take a long time. This game took 5 years to complete and they had a ton of work to do. So my theory is this, what if they received some sort of payment to include her in smash and then they used that money to make the extra mode. Its very tinfoil-y but it has been on my mind for the past couple of days.
The next thing that comes to mind is the sales record of HGH on the Switch. While the success of the game would not play into the base roster, i believe it would certainly bring her into the realm of a potential DLC character. HOWEVER, Nintendo is already quite aware of Pirate's Curse's success, enough for it to appear on the front page of the Eshop for A REALLY FLIPP'N LONG TOME as well as showing her on the cover of Nintendo Power. Nintendo definitely knows she exists and is a financial force to be reckoned with. Her name = sales for fans. I'm buying Indivisible SOLELY because she is in it. Heck the only reason i got a switch a few weeks ago was because I realized the potential for our girl to be in the game. Nintendo will have sold me the game if she is in it.
The last thing i can think of it the fan-art by that one guy who's name i cannot pronounce.