While ordinarily, women do not just "dry up," and a mom who is nursing frequently almost always has milk, no matter what the pump is telling her, there is one MAJOR exception to that. Pregnancy does dry up most women's supply. It may not completely dry it up, but for many women, it does. So it is very very possible that in fact, your daughter's milk is drying up. It is sad! I'm sorry. This is one aspect about getting pregnant that I feel like a lot of women are not really warned about (partly because breastfeeding is still not the norm in our culture). It can cut short your nursing relationship with your older child, unfortunately. Sorry!