When can I start giving my baby cereal in her milk?

I started at 5 months

6 months is best unless you speak to your pediatrition and he gives you the okay for any reason

6 months is the recommended age to start any kind of food

The article @jennatess linked you to is actually perfect!

It's not good for them unless they have reflux. It ruins the mechanism that tells them when to stop eating and they end up overeating without realizing. It can lead to a lot of issues in the future.

http://wholesomebabyfood.momtastic.com/tipcerealinbottle.htm