To find the open port on your computer use the netstat -a command in CMD or COMMAND prompt. Look for any suspicius ports open and close it with you firewall. Get a good IDS (Intrusion detection system) like HoneyBot, that might work. Go to ur startup folder and look for a batch file that execute when windows start, if there is one, find out what it does by opening it in notepad and if its harmful then delete it. Maybe there is a trojan on your computer that opened a backdoor for her.