It could be it's the porridge that's causing her to have less. Really milk is more important than food until a year, so you might consider just cutting that out as she doesn't need it. But really, babies don't always finish their bottles. In fact, my daughter rarely has (and she's almost never had a 9 oz bottle and she's 1), so she's having quite large amounts during the day. Just see how things go. It's always going to be changing though. That's how babies are. If you see her decreasing amounts in the long-term though, I'd cut out the weaning and just focus on milk.