Before opening the attachment, Natasha should not open it directly. The best safety measure she can take is to scan the attachment with antivirus software or use an online virus scan tool to check for potential malware. This will help ensure the file is safe before she considers opening it.
In the options provided, forwarding the email to colleagues for their opinion is not the best option because it still poses a risk of spreading potential malware if the attachment is harmful. Disabling the firewall is also a bad idea because it lowers the security of her computer. Overall, caution and proper scanning protocols are crucial when it comes to unknown attachments.