Re: Lactose overload?
I don't know how things work with exclusive pumping, but you're right around prime time for a growth spurt. And you're right, the bright green stools sound like a foremilk/hindmilk imbalance.
Is there any reason to exclusively bottle feed? Maybe it would be easier to regulate the milk with nursing?
I'm sure that you've already seen the info on how to resolve an oversupply issue with nursing - which leads to the foremilk/hindmilk imbalance and then the green stools, unhappy baby etc. I imagine that it works the same with exclusive pumping - so only pump one breast each time. When you pump and dump the other side you're telling your body that you need that milk. So - block feed, or block pump in your case, by pumping on only one side for each feed. If that doesn't work, then stretch it out to pumping on one side for two feeds and then two feeds on the second.
ETA: It may take more than one day for her supply to regulate. I would keep trying for a while and stop using the formula, but that's just me.
Lilah 10/08 nursed 25 months
Beatrix 01/11 nursed 30 months