Some kids do not have to be 'transitioned.
My exclusively breastfed Daughter, went from breastmilk straight to whole milk at 1 year old, with NO problem. Even if I was still nursing her. She had both.
She self-weaned from breast, at about 2.5 years old.
My son, would NOT take whole milk. So for him, I had to mix part breast with part whole milk... gradually. One ounce whole milk and the rest breast. Gradually. And he had self-weaned from breast at about 1 years old.
He has very picky taste buds.
Nursing before bedtime, at this age, is to me... NO big deal.
I nursed both my kids before bed and naps, even at that age.
I see nothing wrong with it.
But since you are doing that, her nursing only at bedtime is really hardly much. Just do it gradually. Night time, is the hardest to stop.
So I assume, you are giving the rice milk in a bottle? Or in a sippy?
The thing is: you do not 'have to' stop nursing, just because she will be taking other forms of 'milk' and she is going to be 1 years old.
But it is up to you.
There are many different ways, we Moms, introduce other milks to our babies. It is up to you.