Pumping breastmilk for DAD in OA

I breastfed my daughter, who was placed with her adoptive parents on the same day I was released from the hospital, and around a week after that (I had been providing breastmilk that entire time, with a pump that the APs had bought me), I came to Mexico to visit my other daughters, until the 10th, and all this time I have been pumping, though not as much as I would have liked, since my milk supply has gone down. I plan on pumping until my DAD is at least one. I was just wondering if anyone knows around how much milk I need to be pumping? She will be 3 weeks when I return.