Don't think of a sentence with piace, piacere, piacuto etc as representing "likes" but rather "is pleased by". So this is "to her, she is pleased by, it, immediately" which isn't a valid English sentence but is the way it is constructed in a sense. So the first part, "to her" can either be 'a lei' or 'le'; the second part is 'è piacuto'; the "it" is unknown but must be a masculine thing, since it is piacutO and not piacutA. Then 'immediatamente' goes on the end. Hope that helps.
Is the reason she liked "it" as opposed to "him" or "her" related to the "o" at the end of piaciuto?
The "o" ending means that she liked something that is grammatically masculine and singular. So it could be a "him" or "it".
Would this not be "Lei" rather than "Le" or is it being used more in the way that "lo" or "la" are used before a verb?
if "she liked it immediately," why isn't it "è piaciuta" since when you conjugate verbs with essere they take on a gender?
In "è piaciuta" it's "it" that is feminine. Very possible, but it has nothing to do with "she" (that's "le").