The presence of women is a fundamental and important element of understanding the true philosophy of Karbala. As for the precise number of females in the camp of Imam Husain (a.s.) in Karbala, there is no exact consensus for this.
In one reference (al-nafas al-mahmum) it is said that there were twenty, being either wives, mothers or daughters.
Here are two links (in Arabic) that give detailed description of this analysis:
With prayers for your success.