The movie had to try to explain the character's hatred of Dalmatians and this is what it went with: Cruella's mom was actually killed by a pack of vicious Dalmatian dogs when Cruella was young.
The answer, as it often is with Disney movies, is a dead parent. How do you get audiences to understand why Cruella hates Dalmatians so much that, in the animated classic, she feels no compunction about killing them and skinning them for coats? How do you get people to be on her side? ( Spoilers ahead) We always knew it would be tricky for Disney to portray Cruella de Vil in a more sympathetic light, which it set out to do in the recently released 'Cruella,' the live-action film starring Emma Stone that chronicles the early rise of one of Disney's most iconic villains.