There is an easy way to do that right in Gmail. In the settings tab, go to settings and first add a forwarding address under Forwarding and POP/IMAP. Enter the desired forwarding address and confirm it by entering the confirmation code or clicking on the confirmation link. Then go to the Filters and Blocked Addresses tab in settings. On the bottom of the page choose "create a new filter". In the first line enter the email from the certain sender that you would like to forward, then click on "Create filter with this search", which will bring you to the next page. Here check the "Forward it to: choose an address" box, and choose the address.
That should do it. Gmail has great filters for mails
Hope this is helpful, might not be Automator or applescript, but it's right inside gmail, fast and easy... cheers