She's correct that she can take her brand and her trademark and leave, and he can't use it.
She is absolutely wrong that "anyone else" could do Ryan's actual part of the work in the business. The man has a degree in exercise science and it has been his career field ever since. He is actually qualified to write exercise plans, adaptations to exercises, and meal plans with balanced nutrients. None of Whitney's friends have those qualifications. Not even Jessica lists what her certification actually is - NASM or ACE would be the accredited ones - and there's no degree listed either.