I really think 5 months is too young for solids. I can't believe there are pediatricians out there recommending solids that early.
My son is 8 months old and isn't eating solids. We have intro'ed them, but he's not terribly interested. I nurse on demand so I'm not worried.
All babies seem "ready" for solids. You could put rat poison in front of her and she might grab at it as if she wanted to eat it. That's just a developmental skill they have, it doesn't necessarily meant she's ready to eat.
Skip the cereal...it has no nutritional value that she isn't getting from her formula.
We started with avocadoes, banana, sweet potatoes, etc. My 8 month old has tasted peaches, cherries, potatoes, bananas, and apples.
Check out the website http://www.wholesomebabyfood.com/
If you eat fairly healthy, whole foods, there is no reason for your baby not to just eat what you eat. And I can guess that none of you are eating rice cereal for dinner! :)
Ignore the pediatrician.