@BCS
I believe she bowed to her husband as gratitude, because she decided to leave the care of her daughter entirely up to him and move on.
Also, if you read the conversation after the birthday party between her Mother-in-law and her husband about 'her decision', it seems the birthday is probably the last time she will see her daughter.
Previously, she was always reluctant to talk to her daughter, and she actually hardly interacted with her daughter other than the monthly meetings. Even buying the large teddy for her made her feel as though she was intruding into her life, as though she already decided she wouldn't do it.
The fact that her daughter came looking for her, meaning she didn't meet her after she moved and didn't inform them that she moved away. Looks like she moved on for good.