As well as Parentification, Narcissistic Mothers can also practise a form of Infantalisation, i.e. keeping their daughters young and dependent on them. This is so the daughters will never leave them to being their own adult lives, and so will remain around to provide lots of lovely Narcissistic Supply.
This can be done in different ways. Perhaps the mother will forever tell the daughter, to the point of brainwashing, "You'll never amount to anything, you'll never survive in the real world, it's just as well you've got me to mind you."
Another method of Infantalisation is to constantly overstate the dangers of the world, so that the daughter thinks the world is an inherently unsafe place and that the only protection is via her mother. This further creates a dependency. There's such a huge cost though, because the daughter never, ever feels safe, perhaps not even in her own bedroom at night - because bad guys can break into bedrooms at any time.
Now, I know, of course, that bad things do happen, and that there is a danger in the world. I know that most of us work on a false assumption of safety, because that lets us function. But the truth is much more towards the safety end of the spectrum - the odds of any one bad thing happening are miniscule. The mother who terrifies her daughter about being abducted from her bed will happily take her daughter out in the car - where there is a real, albeit small, risk of injury and death.
Infantalisation isn't about genuine protection - it's about creating terror and dependency.
It might take the form of giving money to the daughter, constantly re-enforcing the message that the daughter can't make it on her own. Of course this money has huge strings attached. It's possible too, that the daughter genuinely cannot really manage her money, or look after herself properly, as she was never taught how, and was brainwashed into thinking she couldn't.
Maybe the daughter has been trained to ask the Narcissistic Mother's advice on everything, which keeps the daughter dependent in that way, and also makes sure she's doing everything in reference to her mother - again, the Narcissistic Supply!