I don’t think there is any issue at all with parents going on holiday childless IF the child is well
Cared for back home, has other opportunities with you to make memories, go holidays etc. I really believe that parents away alone can be positive and contribute to healthy parents. My parents would go away without me when I was young but I was left with my gran or aunt and I would have the best weekend/week ever. I’d be spoiled, taken places, special dinners. I was never ever sad they went because I knew that they would be taking me somewhere in the near future too. However we all know that these children have not had these experiences with their mother, we know that when she has them in her care they are in a constant state of fight or flight. There is no big fun days out, kids holidays to the tacky nightly entertainment or the tacky hotel splash park. And that’s the reason I would say she’s selfish, not just the simple fact she has went on holiday.