Tambo, she could have got a mortgage if she had an income of her own and she had automatic custody of the children, which is why Lucan went to extremes to have her declared insane so that the court would award custody to him.
When she played clever and admitted herself to the Priory she proved she was sane and got custody back.
Lucan didn't want to divorce her because she would have been awarded the house at least until the children grew up and custody of the children, which is why he tried to kill her.
She is probably estranged from the children because they don't believe he murdered the nanny and she believes he did.