From the little understanding of French I know and I must be clear I am not a native French speaker or writer, the English meaning of these two sentences in particular might benefit from a more literal translation.
“I’ve made the link between you and her. You alone, from now on, [must] help her with the rest.”
[must] suggests the implied demand, direction or request, which the sentence is.
[Her] could alternatively be it (le or la). The e or a is silently dropped. However elle (she) is specifically female, so can assume l’aider refers to the pronoun la (her). I think it is worth making the distinction if we are talking about possibly Emily or some other entity, it, which Emily may now be.