How to write a moral letter for a army moral waiver?

I am a Army prior service wishing to get back in the army. I have to write a letter explaining why I was chaptered out. I received an article 15 for improper relationship, at the time I was a single parent and the the hardship from the article 15 (i.e. financial difficulities, multiple AER loans) forced my chain of command to chapter me out) I received a misconduct w/ under honorable conditions, but after going before the Army Review Board it was changed to Secretarial Authority w/ honorable discharge,becasue of my years in service they said I should not have been chaptered out before going before a review board. I guess I am asking how I can right a good positive letter, usarec will not deny my enlistment, can someone give me examples or ideas?