A mother supplementing a 6 month old who is currently breast feeding with a
supplementer bottle (breast milk), she is not sure the supply of breast
milk will be available and was wondering if she could use RICE MILK, is
there any problems with this?

Why doesn't this mother get her child started on eating family foods (and
drinking water) along with drinking breastmilk? from six months other foods
are fine as long as there are no allergy problems, and the kid is meant to
learn to eat in a variety of ways, not all from a bottle or breast or
supplementer...Why does she want to add supplement via a nursing
supplementer anyhow?

Foods other than breastmilk put through a nursing supplementer, and so
bathing the breast in the food, can quite readily lead to areolar eczema.