It is hard to ignore the fact that Rosalind is the true focus of this excellent comedy and that Celia is a lesser character in comparison with her cousin. She is characterised by her deep love for her cousin, Rosalind, and her unmatched devotion. Note how she responds to the banishment of Rosalind:
Shall we be sundered? Shall we part, sweet girl?
No, let my father seek another heir!
...For by this heaven, now at our sorrows pale,
Say what thou canst, I'll go along with thee.
As such, she is a character who plays "second fiddle" to Rosalind.
It is Rosalind of course that is the most fully realised character in this comedy, outshining both Orlando and the observations of Touchstone and Jaques in her wit and wisdom. Part of her success as a character lies in her desire to fully engage in life and the way that she is happy to criticise both herself and others. She is able to play many different roles and give voice to many different opinions, and it is this ventriloquism that makes her such an enduring heroine of Shakespeare's work. Celia acts as a kind of sidekick, who does have value in herself, but is overshadowed by a greatness with which she cannot contend.