I have a female GT in a 4'x2'x2' 120gal tank with an L397 pleco. I did have black widow tetras with her as well but had to remove them after she killed one. They lasted a couple of months with no problems then one day out of the blue BAM! Dead tetra.
My female is about 6" long. I wouldn't put another cichlid in with her as I believe she'd try to kill it. She tolerates the pleco because he stays on the bottom, any fish in the actual water column better be ready for a fight.
In a 6' tank you may have more luck with tank mates than I did but make sure they are either really quick and have somewhere to retreat where the GT can't get to them, or be prepared for a massacre out of the blue and to separate. It may not happen, but there's a higher chance that it will.
Why not instead of cichlid tank mates try a pair of GT's and some larger dithers like swordtails, tall bodied tetras, etc? Just make sure you have a large enough group of dithers, I only had 7 widows in with my GT which wasn't enough to confuse her and she nabbed one.
Whatever you decide mate, good luck!
TL;DR? Be careful putting tank mates with terrors, there's a reason they're called "terrors"
Disclaimer: I do not know everything, nor do I claim to. This is my opinion based off of my experiences. Results may vary.