What does wollstonecraft mean when she says that women should become more manly, or masculine

Her writings were excellent. 
She was not referring to physical featuresshe meant take upon ourselves (or the women from her era), the aggressive charateristics that men displayed concerning their rights, liberties and privileges. 
Men made sure they put laws in place to work for them, protect THEM, serve THEM, but the women were literally made to be economic slaves to them. Mary asked women to stand up and be heard, take part, silently or loudly. It was time to rewrite our own bill of rights and demand that women have a right to their own property and money and children. Because up until that time, men could divorce women and leave them peniless. 
she also asked us to leave behind meekness and naivete and nurture confidence in our behaviors. to wake up and not place our destiny into a mans hands and look to him as Lord and master. The change had to take place mentally first.