OP, I strongly suspect she has PND, which is manifesting itself in her old eating disorder ways. Do not be so quick to dismiss her saying things like having your child is the biggest mistake she's ever made. Of course she loves her, and is a good mum, but she sounds very overwhelmed and conflicted. It is clear that her ED has returned - it doesn't matter that the last time she was noticably ill was in the 90s, it is something you live in recovery with, like Alcoholism, etc. You don't ever get rid of it totally.
And babies CRY. She is not inadequate because her baby cries. Although, if she is not eating enough, she will be weak, emotional, exhausted, foggy-headed and moody, and this will affect how well she mothers her baby,mand how well she copes. If she is punishing herself through not eating, he will be punishing your DD more, because she is not getting all of her mother, she is getting an ill and emotional mother who is fixating on something outside of the baby, when all or most of her attention should be on your child right now.
On a practical note, is she breastfeeding? Because if she is, and she is starving herself (let's call a spade a spade: this is not 'skipping meals', this is starving herself), then it will be seriously affecting the flow, quantity and quality of her breastmilk, which will be bad for your DD.