Yeap, the idea was that like the rest of her body evolving from the parasite toxin to be more lewd, the futa side will also conform to bigger sizes, although she would have to undergo some rough training to achieve that :3 (for story mode)
For the animations and gallery type sake (free mode), i guess she will need to control it's size at will via some extra magic.
It would be funny if you had to use the Konami Code in order to activate it during Free Mode.
But I will assume that it will be related to H-exp and a new skill, right?
Also, as a test, you could try to see how compatible is with non-tall females by reusing the Birthday Event Animations with the nest females with similar animations, like:
-Bunny: TC's anal
-Harpy: Blondie's thighsjob/Vaginal
-Slime: since she has a rigging for oral sex
