I guess I always assumed monster girl was like a snake lady, harpy, etc... but I guess Lilith could fit that definition.It's fine it's totally up to you. People just thought the monster girl tag might help people that search for those games to find it easier. The tag in particular has been growing more and more popular lately. Seems like a lot of devs are switching to the 'I live with my landlady and roomates and nothing out of the ordinary happens" settings to introducing fantasy or sci-fi elements that often have monster girls or alien chicks in it. Even Oppai-man who has like the most popular patreon out there(seriously i have no idea how he is making that much money) released a fantasy game recently with elves and succubi and all that.
Great times for me personally as i am loving the fact that more and more people are moving away from the boring, quiet suburban stuff that devs like ICSTOR popularized.
A part me wants to imply that Lilith doesn't necessarily look how she does "naturally" and that she may have a more "true" form... but that's just an idea at this point.
I do also want to do a lot more with the fantasy element and the next chapter does delve into it more than Chapter 5 did.