Actually, Sarafina is one of my favorite characters in TLK...
She's so beautiful! Eventhough her role is very small in the movie, we can see her more in books and comics. She seems to be a gentle and caring mother; Nala is very lucky. I'm not sure why so many fans are so interested in Sarafina... Maybe because we don't know about her so much. Many artists in TLKFAA (including me) have created stories for Sarafina.
I don't believe that the "My, how you have grown!" lioness is Sarafina, eventhough she has the same voice. In the original, English version, maybe, but not in other versions. If the lioness was meant to be Sarafina, she would have Sarafina's voice in other languages, too.
I mean, in the Finnish versions of TLK and SP, Sarabi and ZIRA have the same voice!