R.M.
Just take it away.. Throw it away at night when she is sleeping. Let her know big girls drink from regular cups now.. Do the same thing like if you weened her from bottles to sippy cups..or bottle at night when she was younger..
My daughter yelled and screamed for 2 nights when she no longer had that bottle at night as comfort..so when she transitioned from sippy cups to regular cups at 3.. we had no problems