Hi Pashmina,
How does Website A is a redirect to Website B and can it has one page indexed?
If Website A has a 301 PERMANENT redirection to Website B, then I think it should stay permanent.
If Website A has a page indexed, then I presume it is not a 301 redirection. In that case, moving the content and making a 301 redirect from Website B to Website A would be a good idea in term of SEO.
But, you shouldn't only think in term of SEO, you should also think in term of branding and usability. What is the domain name that reflects your brand? relates to your products? is easier to remember?
Best regards,
Guillaume Voyer.