Her argument here is difficult to follow. The passage reads:
"...yet when a man seduces a woman, it should, I think, be termed a left-handed marriage, and the man should be legally obliged to maintain the woman and her children, unless adultery, a natural divorcement, abrogated the law. And this law should remain in force as long as the weakness of women caused the word seduction to be used as an excuse for their frailty and want of principle; nay, while they depend on man for a subsistence, instead of earning it by the exertion of their own hands or heads."
As far as I can tell, the exhortation goes as follows:
Unfortunately, contemporary women are weak in moral principles and financial resources.
Women can and should be strong in these respects.
As part of their empowerment, pregnant unmarried women should stop blaming their "seducers" for the sexual activity in which both parties willingly participated.
(Implied) If men do not enjoy providing for their lovers and their offspring, then they should admit that women have sexual and financial responsibilities, i.e. assent to Wollstonecraft's feminist platform.
It is unclear to me how the claim that pregnant unmarried women should stop blaming their "seducers" is compatible with the idea that men should provide financially for their lovers. Wollstonecraft critiqued the contemporary assumption of her wealthy economic class that men were expected to earn money for their families while women were expected to sit at home and look pretty, and she envisioned a future in which women took responsibility for their own lives. The present and the future visions are clear, but her intermediate step--the specific practical recommendation by which the society would arrive at a more perfect future--is not clear at all. She said that men should provide for women until women got sick of the attention and, perhaps, if I read her correctly, until men became feminists (ceasing to use the word "seduction" as an excuse for women's behavior). We need a better-detailed program for social change.
Mary Wollstonecraft. A Vindication of the Rights of Woman. (1792) Chapter 4: Observations on the State of Degradation to Which Woman Is Reduced by Various Causes.