I think she and/or the label are holding back the second single because they know it will flop. Boyz wasn't a hit but it got a lot of (negative) attention. This new song will sink without a trace. The label probably know this and want to delay it happening for as long as possible because after there will be a lot of finger pointing for who made the expensive mistake of signing her.
I still wonder if it's a case of the right time for free marketing having passed, so needing to wait for the next round.
With Boyz and its surrounding situation Jesy wasted a lot of very well planned and timed marketing - she had a lot of remaining good will from her documentary and using similar wording in her announcement of leaving LM, had the momentum and interest factor of being the first of the girls to go solo, and they timed it close to but not in direct competition with Between Us - timed well to use LM to boost Jesy in the tabloid media without risking the PR drop of being outsold by them.
Between blackfishing, managing to bungle the "Leigh Anne attacks Jesy" headline they had handed to them, the song not being saved by two high-profile samples/cameos, and Jesy making basically no effort to promote it, a well planned marketing campaign was squandered.
It seems like Jesy got used to having a built in audience and being able to opt out of promoting her music because the other girls stepped in whenever Jesy wasn't feeling up to it. She either needs to learn to face the criticism and actually work to promote her music, or give up. All the expensive stunts in the world from her record company and management can't overcome the talent not being willing to do their part.