How often does she have her child, if you don't mind sharing.

Most parents can attest to a significant difference going from one child to multiple children. Your children already came as multiple, so this is a huge adjustment.

Schedules and keeping to a rigid sleep schedule can help with ovwhelming feelings of this can't be happening that she could be feeling. That is, if she's willing to take a good look at herself and is wiling to accept an overwhelming responsibility.

If she is inflexible and unable to grow and mature, you may very well be left with a huge mountain of resentment towards her.

I know from experience it takes a lot to overcome the feelings brought out about looking at your own children as an out. It's an excuse. Supportive partners would try to come up with a game plan.