A couple of friends of mine, put band-aids over their nipples and explained that Mommy had a boo-boo or that their milk was broken.
They said this worked for them, totally.
Your child is only nursing 1 time a day. So she is really actually self-weaning.
But yes, try giving her a cup of milk before bed instead.... many kids do like that even at older ages. Nothing wrong with that.
But the thing is, she may or may not like milk from a sippy cup.
Or, since she only nurses that 1 time a day, out of "routine"... then switch up the routine. Meaning, unless she blatantly asks you to nurse, then don't... or, make like you are busy and just say "one minute, Mommy is busy..." then make yourself busy. My daughter self-weaned at about 2.5 years old... and that is what I would do, to change up the "routine." And she was fine with that. Then the child usually gets distracted with something else and "forgets" they asked to nurse.
Just some ideas,
All the best,
Susan