Answer:
Vocally? Christine Daae was an extraordinarily gifted singer as a child, but when her father died her soul went out of her voice, in a sense, and she could only become a chorus girl at the Paris Opera. Once, however, the Phantom began to instruct her, her performance quality increased dramatically and she became very successful at the Opera; she earned the lead role of Marguerite in Gounod's Faust.
Of course, she was no longer an operatic success when she left the Opera and ran away with Raoul de Changy to Sweden.
In her life overall? That's another matter entirely.