Make sure you have a weapon equipped. Then just echostrike her uvula and attack the tongue. This strategy should work even without any stat boosting items.
If you're really struggling you can go around Part 3 and collect all the stat boosting items. Their locations are in the guide too.
I recommend reworking kurakawas infirmary moment, since no matter how many times you interact with other parts of her body only mouth would increase higher than all other parts, also since the game has gotten popular and you have gained higher support, you can't just be only Dev working on the game can you? Since the project has gone so big and there are so many stuff to work on while you're also reworking the older versions.
Since if you're still alone that's gonna put a lot of toll on you.