Traditional views would have us think that women are like ivy, a plant that tends to cling to other stronger plants in order to support itself. In other words, people think that women should cling to men the way that ivy clings to a strong tree for support.
As Wollstonecraft writes at one point, "it might be proper, in order to make a man and his wife one, that she should rely entirely on his understanding; and the graceful ivy, clasping the oak that supported it, would form a whole in which strength and beauty would be equally conspicuous" (2.13).
Of course, she doesn't actually buy into this metaphor. She's just outlining a popular, wrongheaded thought that continues to hold women back. However, Wollstonecraft does believe that without a proper education, it's necessary for women to use men in order to climb the social or socio-economic ladder much in the same way that ivy has to climb a stronger tree in order to grow.
Women are forced to act like ivy, rather than being naturally predisposed to act like ivy. Women in Wollstonecraft's time had no other recourse but to rely on men's strength. However, if women were given proper education they would be able to grow on their own. They'd have the strength to grow independently, like a dang oak tree.