Is a woman considered sinful and in breach of her agreement if she asks her husband to move in with her after she had agreed to live separately from him for long periods, due to her psychological suffering from the separation?

There is no blame upon the wife if she demands her right to equitable division, even if she had previously waived it. The husband is obliged to be just between his two wives regarding overnight stays, or else divorce her. He must fear Allah and be just between them.