Re: does my baby ever need a 5 oz bottle?
Maybe one way to look at it is that even if she really does want the 5 oz at a shot, it's really not going to hurt her to be short an oz occasionally, and you'd rather be getting that extra oz "from the tap" - especially given you're coming in to feed at lunchtime. And DJsmom made some good points about things that might be concerning in the short term. So better to err on the side of less than more. But if you're really convinced that she's hungry after the 4 oz bottle (and not just a little fussy or willing to eat more), I say go with what works.
I like the idea of freezing it to make it that extra step - even if you trust the DCP. Just to have that extra check against misinterpreting "willing" and "needing".