She’s trying to help her cousin become a functioning member of society, but her mother clearly doesn’t want that. 

No parent likes to hear their child crying. There’s a reason the «cry it out» method that dominated the 20th century feels unnatural to parents: it probably is. If a newborn is crying, it’s natural to want to comfort them and help the crying stop. No parent can hold their child literally every single time they cry, especially if they have other children to attend to and a household to manage, but there’s a difference between letting your baby self-soothe most of the time and having to let them cry while you cook dinner and make sure your toddlers don’t hurt themselves. 

Toddlers and babies are totally different. They might both cry to get something they want from their parents, but a toddler is old enough to learn that screaming and crying are not acceptable ways to get what they want. A baby cries because they have, quite literally, no other way of communicating their needs with their parents. Toddlers are not manipulative monsters, but they certainly act like manipulative monsters. It’s a parent’s job to teach their little kids that they won’t give in to screaming, crying, or carrying on. If they give in to a kid who cries over not getting ice cream, that kid is going to learn that crying for ice cream is a surefire way to get their hands on it.