Honestly no, the 55 is already too small for her in the long run so adding another cichlid inmate is only going to cause problems with one killing the other or they become a pair short term and you end up with hybrid fry, pick a species that can't cross and then you run into the aggression issue where the spawns fail and the "pair" break down resulting again in the potential death of one or both. I understand you want to add another cichlid but generally only having two within an aquarium fails, they pair regardless of sex or one with get killed/rehomed. With the wife set in stone on keeping the festae wet pet as others suggested is the least likely to fail. Dithers won't have the room to escape the belligerence so are more than likely also short term inhabitants.