I think Xena is a classic case of "Failure to Thrive." For whatever reason (genetic), she is not healthy and doesn't have the drive to eat. I suspect it has a lot to do with the inbreeding it took to get her "fancy" colors and such.
For now, she's in a sick tank and I'll force feed her Critical Care twice a day to see if we can get some nutrition into her. Some times babies get so depleted that they don't have the energy to eat and then they just spiral downwards. Or, it's possible, the nutrition will expose a genetic flaw internally that will end her life. It's hard to say at this point. Only time will tell.
Babies are tricky. An unhealthy mother or an undernourished pregnancy and pre-pregnancy can create deficits in the babies that no one can over come. That's why education is SO important before breeding!