I just found this game like a week or 2 ago and the character creation/transformation is definitely made well and definitely made for specifics and any npc. I can see how this can be difficult to code and to lay out.
If you look at the transformation tab for any character that can shape shift, each section of the body has its own variables, descriptors, and functions. The ovipositor and spinneret would most likely have a capacity and production limit much like the penis and breasts. Its going to come down to the limits and other applications for those parts (the spinneret possibly having a combat functionality like the horns and tail).
But I also think that she is also going to be working on limitations for certain species as well, which will also take up some time. The only reason I am saying this is a glitch I had making me able to transform imps (which they shouldn't be able to do). The imps can only change there height from 61cm (24in.) to 121cm (47.6in.).
If this is the case, the transformations for the slimes and Lilins are going to have to work differently. The slimes are described to have limited transformation capabilities while Lilins are described to have unlimited transformation capabilities. Lets say the slimes are only able to access the overall general transformation abilities (lets say the current transformation screen), while the Lilins on the other hand can access the other species locked off stuff (going from 61cm to 366cm rather than from 122cm to 366cm). Half demon transformations seem to be pretty good so far however.
Lastly, I do think this is the case due to Lyssieth's hair being described as slimy when in the transformation screen for her when you import her as a slave and also seemingly costs about the same as a slime.
(Sorry for the rant, I like thinking out loud.)