Tell the mom to take a small 2 oz plastic bottle (with nothing in it) and put a regular nipple on it. Let her baby play with it, as a toy. Once she sees baby is comfortable putting the nipple in her mouth, put 1/2 oz of breastmilk in it. Baby will discover on her own that it's a feeding method. Just don't pressure her.
If mom wants to try something different, have someone else give the bottle (warm, not hot) to the baby about a half an hour before you expect her to get hungry. Mom will need to leave the room or house, so baby will try. It's like asking a starving person to use chop sticks. Offer it casually, when baby isn't hungry, upset etc. Two frustrations (hunger and learning a new skill) prove too much for babies and then they don't take it.
Let us know how it works out for her.