One reason I wanted to reprint your letter is because I hope it will encourage parents to be more thoughtful about the way they treat their children. It's easy to favor one child over another (often without realizing it) but the results can be very harmful.
One example in the Bible is Joseph, whose father, Jacob, "loved Joseph more than any of his other sons, because he had been born to him in his old age" (Genesis 37:3). But Joseph's brothers, filled with resentment, kidnapped him and secretly sold him into slavery in Egypt.
Many years later, however, they went to Egypt to buy food and unexpectedly met Joseph. What was his reaction? Instead of exacting revenge on them, he forgave them. And what was their reaction? At first they were fearful, but then they accepted his forgiveness and were reconciled to him. Joseph refused to be a prisoner to the past.
What is the point? Simply this: When something hurtful happens to us, we have a choice. We can either be filled with bitterness, or we can turn our bitterness over to God and ask Christ to fill us with His love. Ask God to forgive you for your sins, and then ask Him to help you forgive your mother in the same way freely and fully, in spite of the past. And don't wait for her to call you. Call her first, and go see her whenever you can.