From Wikipedia:

Vincent Canby wrote in his original New York Times review that it was "as if Jenny was suffering from some vaguely unpleasant Elizabeth Arden treatment". Mad magazine ran a parody of the film ("Lover's Story") in its October 1971 issue, which depicted Ali MacGraw's character as stricken with "Old Movie Disease", an ailment that causes a dying patient to become "more beautiful by the minute". In 1997, Roger Ebert defined "Ali MacGraw's Disease" as a movie illness in which "the only symptom is that the patient grows more beautiful until finally dying".

😄

Wikipedia article: Love Story (1970 film)

According to what I've read online today, it can be concluded MacGraw's character dies from never-outright-specified (other than in the corresponding novel) leukemia.

I watched the movie on network tv when it had its broadcast premiere in 1972 when I was a kid, so no longer actually remember anything about it at this point, half a century later, beyond that Ali MacGraw's character is diagnosed with and dies from some fatal malady, and that this film was the box office megahit of the day.

Film critic Judith Crist called Love Story "Camille with bullshit". 😂