I have had mixed outcomes with training. My first one (my avatar) was very hard to train. It took nearly 2 months - and it was quite annoying. Luckily, at the time, I had the time for this. I began by feeding frozen bloodworms. Once he accepted those, I mixed bloodworms and baby pellets by creating a clump of soggy pellets and worms. He eventually took this. Then, I started putting pellets into the cup I was thawing bloodworms in. This let the pellets soak up the bloody water. Eventually, he just started taking regular pellets.
My others were much easier. They were starved for about a week after 2 weeks on frozen bloodworms and they immediately ate plain pellets. After that, fish (redbreasts and greens) got easier b/c they learned from the other sunnies in the tank that pellets=food. It certainly helps to have other trained fish in the tank. Don't be afraid of making them fast for a while.
Sorry for a long post..
Your fish looks like it could be female. The earflap doesn't look elongate enough. However, it is tough to tell. The black tank (which I like) may be causing it to darken up a bit. But still looks female as the colors are just not intense. She is staying a rather 'yellow' color (typical of females) as opposed to the intense red and blue sheen on the sides that males have.
I think Brian Zimmerman has a pic of a male and female next to each other on his new website.
ZimmermansFish.com