There will be more anniversaries. IIRC Sims 4 has another 5 years, or so I've heard, so that's 5 more years of a yearly gift. And this year they did a free gift for both the Sims 4's anniversary, and for the anniversary of the Sims franchise as a whole. So that's 10 more opportunities for free content.
They could also just do a new Halloween event that gives her to us, or just a Halloween free content thing.
I wouldn't mind paying for her, though.