How do you change UTF-8 encoding to windows encoding for sending to one specific E mail address?

I correspond with a friend in Russia that uses an internet cafe' / translation service. I use yahoo mail and she uses aol. Though she can view the text in my E mail, she can not view the pictures. I contacted the cafe' / translation service and was told that this happens when E mail is sent in UTF-8 encoding and if I will send using window's encoding my friend will be able to view the pictures also. I have figured out how to VIEW messages with different encoding, but I need the step-by-step of how to change the encoding for SENDING to this one particular E mail address. Will someone please explain how to change these settings when using yahoo mail?