I think Hathaway incorporated, rather diversely, a sob, a catch, a whisper, a croak and an exclamation into her performance. It was obviously strenuous acting. But was it relying on the music?
The musical interested me in seeing the 1934 version. In it Fantine lost her front teetch. It was underplayed but, whether despite or because of it I found that Fantine more affecting than Hathaway. Even with subtitles.
Hathaway's performance of course isn't bad. But it's of a piece of the musical Les Mis, which in my opinion just isn't a very good moviie. I suppose the last Oscar contender in this vein was Oliver! People grouse about it winning the Oscar, but it was a much stronger film than Les Mis.