Jack Dempseys usually don't develop a "cranial hump". A fairly reliable indicator is the amount and type of blue spotting on the lower gill cover. Large blotches usually indicates female and lack of spotting would indicate male. Most JD's are somewhere in between but if you post a picture of your fish showing clearly that area of the fish people on here like to guess for you on the sex of the fish.
It is 6" now. And yep, I had just put it in the 29 gallon (for JUST a week, don't worry). It has a very shy personality with me anyways....All the stuff I've done for it in 2 (almost 3) and it still hates meh... :-?
And jeaniel, I actually rescued it from a tank with a 12" oscar, and some vicious african cichlids. It was almost dead when I got it but I put her in a 55 with a nicer male convict, and they actually do spawning behaviours with out all the aggresive liplocking, and charging. She will have ugly fins forever though
If I had to guess I would say female but the JD looks stressed and pretty beat up so that makes it harder to sex.
I find JDs have long memories and when you move them to different tanks or even change something in their current tank, stresses them out and they stay skittish for a few weeks. So my advice is stop moving her and keep her in the same tank and if you do add tank mates, make sure the tank mates aren't anyone who can stress her.