With a 55 gallon 3 species would be good stock. You could up the electric yellow by about 3 more get 2 more acei, and personally I would get rid of the auratus and find another species to also shoot for a 1m to 3-4f. I would also try and get the same M/F ratio on the rest. Seems the common suggestion for Auratus would be more like 1M/6-8F and feel that would take up species slots in your tank since they you would need higher numbers due to their aggression.
If I am wrong I am sure someone will chime in and correct me.
If it's a lone female, and you love the stripes, keep her. If it turns male, the auratus gets rather vicious. I agree with Benjamin above that it's probably best to take her back.
Some red zebras would look nice with the yellow/blue and yellow you have right now, or perhaps some nice albino species for white.