Sometimes it is recommended to rub them with a rough towel, but it's my belief that exposure to the air is adequate. Just wearing a cotton t-shirt without a bra will be beneficial in preparing the nipples. My almost 6 month old daughter is eating no solids at all. She is still nursing every 2 to 3 hours, except at night. I am getting a lot of flack from people that I need to force her to eat.
Breastfed babies can sometimes subsist on milk alone for up to a year.
There is no hurry for you to provide solid food if she is not prepared to take it. Just bring her to the table with you and let her see what mealtime is all about. When she knows she is ready, she'll let you know by asking for what you're eating. He seemed to nurse VERY poorly and I switched him to bottle on the doctor's advice. I know I will be paranoid this time.