Mimi in every version of La Bohème And, yes, despite dying of consumption she's still "beautiful as the dawn" on death's door.
Fosca from the Stephen Sondheim musical Passion suffers from a conveniently vague illness that waxes and wanes according to her mood, but does nothing to make her more attractive; in a notable subversion of the "consumptive heroine" version of the trope, she's ugly, demanding, self-pitying, and doesn't inspire protectiveness in those around her so much as exasperation and mild disgust.
The illness of Eva Peron (see Real Life) is glamorized in the musical Evita. She's made to look beautiful and fragile. Photos of the real Eva Peron from this period show that her beauty was quickly fading. Real death is seldom pretty.
The point of Radium Girls, especially Grace and Kathryn who appear throughout the play. The worst part is that it's based on a true story (see Real Life).
Little Shop of Horrors: Audrey is never diagnosed with anything, but she "is not a healthy girl" and, thanks to being regularly beaten senseless by her boyfriend, has "a black eye...and several other medical problems." Just when it looks like she's getting better, she's mortally wounded by a giant plant.
In a case of Real Life Writes the Plot, Ilse from the revival of Spring Awakening is implied to be ill when she takes off her wig and reveals her bald head. At the time of the Los Angeles production, her actress Krysta Rodriguez was going through chemotherapy for breast cancer.
Little Eyolf by Henrik Ibsen has the title character Eyolf, an eight year old boy, who is crippled and hardly gets to play with the other boys. He dies, of course, by drowning.