Reading about this again today, I can't help think she either has
1. The sort of deep depression that would envelop her almost whoever she was with. After all, she could presumably build some kind of personal life for herself in Monaco if she wanted. She may not have as many choices as she wants, but surely some?
2. And/or an addiction, hence the family staging interventions when they notice she's not well. An addict often chooses the addiction over their children - or may realise treatment must come first.