Remember, males can smell her from several miles away when she does come into season and keep her in your sight. If you do not have a fenced yard do not let her out to potty with out being with her ,it can happen that fast. I would hope you would not do that anyway. Be prepared for the mess. She will,usually,be bleeding everywhere for about a week then the color will change to a lighter shade for about a week,not as heavy, then change back to red again about the third week. This is a generalization, most haven't read the books and may be somewhat different. Have her spayed ASAP if she is a house pet and not to be shown and bred.