Your convict is a female, by the way. Jewel cichlid would probably be a good choice for tankmate, more than salvini (which tend to be really nasty)
I also agree with duanes that some swordtails in there would be a good addition.
If this were my tank, I would keep the convict, and add some A. Nanoluteus. They are like smaller, less aggressive, more colorful convicts. Could probably add 4 in there, plus the swordtails. You will probably get at least one pair, but these guys stay real small (3-4" max), so if you had enough hiding spots for the other cichlids, they would probably be fine in the 55.
Wetspottropicalfish.com has nanoluteus in stock