With an adult female, I would think a kitten would be the best way to go. Maybe it would bring out the mother in her (instincts are more powerful than surgery sometimes
) and she would accept a baby better than an older cat trying to vie for her territory. Be prepared for April to be mad at you for a while.
As far as male or female, some females are so territorial they cannot accept another female. Some males are too rough with the females. Many times when they have been introduced properly, they can get along no matter what sex. I'm certainly not the expert, but I would think, especially if you get a kitten, either sex would be OK.