Daisy, at least to some of the characters, seems almost eternally youthful, a characterization true of the way Gatsby sees her. A "deathless song" might well go on and on. On the other hand, a voice "full of money" is a voice which reflects the kind of life she has lived - Tom is quite wealthy - and her voice reflects that wealth since she is in a different class. I do not think they are necessarily irreconcilable - after all, we are made up of different qualities, many of which might be reflected in our voices.