Apologies if this is a bit long.
My DSD has lived with her dad continuously since the day she was born. He works a flexible schedule at home, was the primary caregiver most of her life, and spends a great deal of time with her, far more than most parents of teenagers have with their kids, and more than her 'traditional household' friends spend with their own bio-parents.
I can tell you that the problem is most definitely NOT a lack of time or attention from DH towards DSD.
I accept that not every case is going to be the same, but since I have the same issue, with a DSD who lives with her dad, as other women on this thread, I think there is something else going on in at least some of these cases.
In our case, DSD has issues with control, and has for her entire life. This is not just my analysis of the situation, but something acknowledged by everyone who knows her and loves her. As I see it now, losing her mom was something she had NO control over, and she was completely unprepared to deal with that. Now she clings even more to the things she thinks she can control. This is a girl who absolutely HAS to hold the remote control when the family watches tv, she physically shakes when she can't.
Our counselour, amongst others, tells us that DH and DSD have a relationship that is too much like a couple, rather than that of a father and daughter, to be healthy. In reading books about stepparenting, I've learned that this is actually not uncommon (as this thread suggests!), and there is even a term for is, spousification.
She hangs (less now than she used to, thank goodness) on her dad like a limpet because she didn't want to lose her position as centre of the household, which is what she was from the time she was a small child. And because this was her way of demonstrating that she and her father were a couple. And, finally, to try to keep control over a situation she could see was changing - my arrival on the scene.
DH and I made a decision together to work on re-establishing a more appropriate role for DSD, one where she can be a teenage girl with the right balance of independence, dependence, security, and boundaries. Besides being absolutely essential for the good of the rest of the household (everyone - me, her brother, her sister, DH - we all suffer when she plays the role of DH's partner), it is better for her. She's growing up, and she can't hang on daddy's neck all the time or share the bathroom with him like a little girl does - but she's also still a child, not his peer, and she has to learn to be okay with that.
The way I think of it, DSD has for years been treated like a toddler, with no responsibilities - but empowered like an adult. It is not good for her, and it hasn't taught her how to deal with the tough stuff, and it hasn't prepared her for a good relationship with a future mate. I sympathize with her, because she is scared and insecure - but the way to deal with that is to show her that she can relax and it will be ok - NOT to give her everything she wants, which ultimately only feeds her insecurity.