This client's daughter currently uses a Nosey cup so that she doesn't have to tilt her head back as much when drinking. However the liquid still comes out of the cup too fast for her and often spills.
There is a product called the Reflo Smart Cup which uses inserts into a cup to only leave a small opening for the liquid which would help this client however it would not fit inside the Nosey cup. This design can be used for inspiration.

Your task is to design a device which is compatible with the Nosey cup and which can limit the flow of liquid in the cup. A new cup design which achieves the same result is also possible. It must be washable and safe to use. It must be rugged and easy to install. Ideally it should have a variable opening which can be adjusted for different users.