[I will provide you with a sample thesis statement that you may want to modify, or use as a guide in writing your own.]
It has been my experience that when reference is made to women responsible for writing about the rights of women, Mary Wollstonecraft has been given the credit. An English woman, Wollstonecraft wrote A Vindication of the Rights of Woman in 1792. It was a literary anthem for many women, though not well accepted by men of that era. With political overtones, it argued for women's rights and equality, receiving a great deal of attention.
In 1845, fifty-two years later, an American woman, Margaret Fuller, also wrote to advocate the rights of women. Trying to soften her message somewhat, avoiding the political, she penned Woman in the Nineteenth Century.
The plight of women can be seen in the following description:
At the beginning of the [19th] century, women enjoyed [none of the rights we do today]: they could not vote,...could not testify in court, had extremely limited control over personal property after marriage, [rarely received] legal custody of their children in cases of divorce, and [could not attend institutions of] higher education. ...subservient to their fathers and husbands... [their] occupational choices were also extremely limited. Middle- and upper-class women generally remained home, caring for their children and [the household]. Lower-class women...work[ed] outside the home...usually as poorly-paid domestic servants or laborers in factories and mills.
Many women felt victimized by these male-dominated social restrictions, but some women chose to voice their concerns in writing. Wollstonecraft and Fuller are two of the best known.
Where generalizations can be made, however, "the woman question," as it was called in debates of the time, has been seen as a tendency to define the role of women [regardless of social standing]... in negative terms.
Regarding Fuller's writing, she was aware of the obstacles she faced in printing Woman in the Nineteenth Century. While her work was received favorably by great writers (i.e. George Eliot—a woman, Edgar Allan Poe, etc.), the male members of the society she addressed were not as impressed.
Recognizing her indebtedness to Wollstonecraft, Margaret Fuller (1810–1850) subtly alludes to Vindication in Woman, though she is careful to distance herself from the political implications of Wollstonecraft's work in order to establish a less controversial argument for the social and cultural equality of women. While Fuller drew her authority from a wide range of writings and practices concerning women around the world, she was only partially successful in muting criticism of Woman.
One of the things that guided writers such as Fuller (as well as Frederick Douglas and William Wells Brown, regarding slaverly), was the writing of Thomas Jefferson:
...it is important to remember that Fuller and others took seriously Thomas Jefferson's assertion that all men are created equal and labored throughout their careers to give palpable meaning to his famous rhetoric.
With all this in mind, were I to write a thesis statement regarding Margaret Fuller's work, I would write something like:
Margaret Fuller was an 19th Century American advocate for women's rights; struggling to be heard in a male-dominated society, she was powerfully guided by an earnest conviction of the truth of Thomas Jefferson's sentiments when he wrote that "all men are created equal."
Hope this is of help.