I am very sorry for your heartbeaking loss of Mia at such a young age.
There are many pros and cons to having more than one Yorkie. Having 2 is twice the grooming and vet care. Having 2 makes going places more challenging. Having 2 is twice the love too!
Does Rosie have experience with other dogs? My first boy Max has an 'only child' personality, but he loves his brother Teddy. They liked each instantly, but we still had some challenges. Having 2 strong males get along is almost a miracle.
I've read the same about having 2 strong females.