Bronte's nappy needed to be changed, but it could wait until after she ate, it wasn't that big a deal. And Louisa got up and got the baby herself, rather than asking Severus to do it. And she was actually speaking to the baby. These were all things that pleased him. However, he was not at all happy with the way she was speaking to their daughter.
Severus wanted to intervene. He wanted to take his daughter and tell her that her feelings were perfectly valid, and that he understood her way of communicating, that he would protect her, and that she was loved. He desperately wanted to tell her all the things her mother wasn't conveying to her right now. But he didn't. He allowed Louisa the space to feed Bronte without judging her methods out loud. Severus could manage that, for now.
Once he had put away the stack of blankets, he retrieved the empty glass on Louisa's bedside table, refilled it, and returned it full of water. She had never said as much, but he had read that breastfeeding often made women thirsty.