She is holding something for certain. Given her age/size if you had a bossy male I would say she’s holding sand, and still may well be. They will pick things up in their mouths, even air, to try to make it look like they’re “not in the mood”. I have seen fronts display this behavior, and my tropheus do it a lot.
You do not have a larger bossy male. These 2 additions are the biggest in the tank correct? 4”? Which puts them in the 2-3yr age range given the slow growth rate of female gibberosa, and in the general sense, not mature enough to produce eggs yet.
So, she’s older than her physical size suggests, she is a crazily anomalous fish, or for some other reason she is practicing holding, defensive or otherwise