The children are not her susraal’s mil’ki’yat. If it is her desire to live alone with her children or with her parents, that should be her decision. As is the decision to live with her in-laws, if that is where she believes she will be happy.
The key is that her life should go on after her husband’s death and she shouldn’t be cross-examined about her actions. She should strive to maintain a positive relationship with her in-laws as her in-laws and the grandparents to her children - but they are not her keepers.