I'm always surprised to hear of abandoned English Bullies, though it is not very often, considering how expensive they are. I'm a Bulldogger myself, my baby girl Betsy just turned two years old.
Glad Rosie found a new home. She's a very good looking girl.
Please suggest your son take her to the vet for a good going over. Bullies have a few health risks not common to other dogs, due to their shape and the breeding needed to get it like it is. Perhaps a health issue caused the former owners to abandon her, though there are so many better/kinder ways to pass a dog off than that.
If your son has any questions about Bully care or what to expect from them in terms of behavior, I'm happy to help, just let me know. They've been in my family longer than me (so >43 years).
As to their faces, well, I think it's ALL other dogs that look odd, never my Bullies.
Alex