There is no real way to set an exact number on this, but you could argue that she was at least 300 years ahead of her time.
Sor (Sister) Juana Ines de la Cruz was born in 1651 and died in 1695. Her ideas about women's rights (which is what she is most noted for in history texts) were much more similar to ideas held by people in the 1990s than they are like those of people in the 17th, 18th or 19th centuries.
As an example, a text that I teach from reproduces part of a poem that talks about the unfairness of sexual double standards for men and women. One passage is translated as
Or which deserves the sterner blame,
Though each will be a sinner:
She who becomes a whore for pay,
Or he who pays to win her?
This sort of double standard in which women are blamed for conduct that is acceptable for men is something that is still around today. Many more people speak out against it than in Sor Juana's day, but the double standard is not gone.
So, Sor Juana seems to be something in the area of 300 years ahead of her time on the issue of women's rights.