[Your letterhead, if desired; if not, your return address]
[Date of letter—month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
I am writing to let you know how regretful and sorry I am for what I said and did not say when we were talking on Sunday. I know you needed me to show sympathy about your illness and about the financial challenges you are experiencing, and it was wrong of me to act so cold and indifferent. I was also incorrect to criticize and blame you for the problems you have been experiencing over the past several months. I know that none of these challenges have been your fault, and I know you need my encouragement and caring now. As sisters, I want us to be close and supportive of each other, not just as family members but also as friends.
I hope you will accept my apology and will forgive me. It would be great if we could get together soon for lunch and to talk more. Just let me know if you would like to do that, and thank you for listening and understanding.
[Sender's first and last names]