Answer:
Yes, Carly Lillian Alba is niece to Jessica.
She's the only child of Jessicas Brother Joshua.
Jessica mentioned her in a couple of videos saying
" Carly is one of those persons, you won't forget after meeting them.
She is very talented and i believe that she is going to be Famous when she wants to. "
Since Carly is denying all request of starting an actinng / dancing career, she is probably never going to be as famous as her Dad or Aunt.
But we are definatly going to hear from her.