N.C.
When you notice she is getting frusterated because she is not getting enough food. I kept wondering why my daughter would cry when she would eat. She wasn't getting the food fast enough. We use advent and she moved pretty quickly out of the slowest flow 1 hole, to the slow flow 2 holes quickly. At 6 months she was ready for 3 holes which is a medium flow. She is almosst 10 months and I swithched her to fast flow, which is 4 holes, and she hates it. It comes out too quick and she was crying again. We moved her back to 3 holes and she is happy. It is just a matter of trial and error. You make think she is ready for a faster flow, but she may not be. Look for her cues, frusteration, sucking then stopping to catch her breath, clenched toes and fingers. (actually in young babies that's normal) She will let you know. Good luck