English Translation
She needs help.
Why isn’t this “Elle a besoin de l’aide.” ?
I wouldn’t be able to explain the underlying grammatical reason other than saying that, because you are saying that she needs help, as a concept, not as a specific thing, you have to use the indeterminate form (i.e. without the " l’ " / " la "). If she required a specific type of help, for example, the help of her friend Tom, you would then add the “la”: Elle a besoin de l’ aide de son ami Tom – notice that it is the same than in english (She needs help / She need the help of her friend Tom) –
Does that explanation help?
I can understand the original question, as French is very fond of partitive expressions. If we wanted to rewrite the sentence, we could come up with “il lui faut de l’aide”, right? But you can’t say “Elle a besoin de de l’aide”, can you?