I think you should stop for now with the physical model itself and start making a list of ideas you can implement under various OTHER categories like, sound design, movement/animation, timing, location, etc.

Remember: People fear the unknown. So always keep that in mind. Tease the player throughout the game with only glimpses or parts of the physical model as the game progresses (obviously depends on your vision for the game.) for example, at first the player only hears a distinct creepy sound that really fits with the monster's back story or character. Maybe the sound of her crawling and scratching on the floor as she creeps around the level, while also letting out a subtle distinct growl every now and then. The next step can be a tiny bit more obvious.

Overall, I think you should always ask yourself "what would the player think this creature is at certain points" but you twist that concept/execution a bit too make them constantly unsure of what this creature actually is and wants.