an independent young adult, so eager to move out on her own and see the world by herself, is turned into a vampire. her human parents are willing to feed her, but now she'll be dependent on them. she can't move away, can't stray too far from the family farm by herself, because she can't be too far from her source of blood for too long. she's afraid of what will happen when her parents are too old to give blood to her, if she'll be able to find someone else to depend on. she'll outlive them all eventually, if she's not left to starve.

a sociable vampire with a wide network of human friends who are willing to offer up their blood to her. they're happy to help her, but she still feels like a monster for having to take their blood all the time. she tries to take as little as possible while they beg her please take more, we hate seeing you so hungry all the time, please let us help. 

But, as in these examples (and especially the "what happens when I outlive my parents?"), it is indeed overwhelmingly about "what if I just can't meet my own needs on my own?" and that is a very common experience.