I don't know whether Chinese girls expect their children's grandparents to look after them, or not. I wouldn't have thought so, as the Chinese are still brought up to respect their elders.
It doesn't sound as if there was much of that attitude from your DIL.
I'm a little confused: is your DIL returning to China permanently, or for holiday?
In your place, I would ring DS up and ask how the new job is and his new home, it can't do any harm to say you are sorry things were difficult while they were staying with you. Just don't sound as if it was your fault, because that is not what it sounds like to me.
Whatever grandparents do or don't do in China, you had explained that you could not afford to stop working to look after the child. I hope you pointed out that in Britain parents look after their children or pay to have someone do it for them.
I hope you do manage to get a more manageable relationship going.
It sounds to me as if your DIL has some serious problems, either adjusting to marriage or motherhood. If you do talk to you son, ask about her, but be tactful, so he doesn't feel you are criticising her.
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