We got Ruby in March 6 years ago and she was three months old and then we got Daisy in December, she was about 6 weeks old and her mum's name was Daisy too. They had found Daisy and her brother next to a bin and the mum was pregnant at the time. They were extremely bonded because Daisy was so young. Ruby just adopted her and took care of her.
Daisy was definitely the one looking after Ruby by the time they came to live with us.