The narrator's husband was a doctor, and constantly chided her for doing things that he felt would over-exert her nervous temperment. He also treated her like a child, and took away anything that might give her pleasure or joy in her life, instead secluding her in a country home with no friends, in a room that she hated, even when she complained against it. Basically, he didn't listen to anything that she said, instead putting himself in the role of superior expert and her as the ignorant patient. It was his decision to:
1. Move them away from all of her friends and everything that she knew and loved into a strange house in a strange country. This completely isolates her.
2. Put her in the room with the yellow wallpaper, even though she hated it and expressed a desire for the more pleasant rooms on the main floor of the house. Putting her up there isolated her even further, and exhibited his unwillingness to listen to her preferences.
3. He forbade her from writing or working. This took away one of her main forms of expression, venting, and healthy mental exercise. It isolates her even more, and forces her to keep her thoughts bottled up in her head without any healthy release; this drives her further into her own delusions.
4. His overall attitude towards her--loving but condescending--made her even more insecure and unsure of herself. She was constantl conflicted with wanting to be a "good" wife and obey, and with her inner voice that knew better. This caused further fragmentation of her personality, leading to the separate identity in the wall.
I hope that those thoughts helped; good luck!