Some great points here. I encourage intervening on your part. Otherwise, ignoring doing so is only going to cause you to fret even more. In the example I gave of my step niece's own inappropriate behaviour I have made some attempts to call into question her own questionable behaviour, "How is therapy going? Have things improved? I notice she is clingy - what does the therapis/psychiatrist say about that? Is there anything to be done?" Yes, I realise this is passive aggressive but it is about all I can manage. It at least is broaching the subject.

Meanwhile, at our family Christmas dinner, my son-in-law (my hero several times over that night) came right out and said something. "How about you stop clinging to your mother's chest and help us out here?" Yay!