technically you're saying "to my daughter, apples are pleasing," so the apples (they) are the ones that are actively doing the pleasing of your daughter, and therefore it's third-person plural.
Could you remove the "le" before "mele".
A mia figlia piacciono le mele. My daughter likes the (specific) apples.
A mia figlia piacciono mele. My daughter likes (generally) apples.
To say that your daughter likes apples in general, wouldn't that be expressed as "a mia figlia piacciono delle mele", ie using the partitive article, as it would be used in French? Wouldn't "le" be reserved for the specific apples that are on the table, say?
delle mele would mean 'some apples' which is the contrary of apples in general.
The partitive is used to refer to a part of the whole.
Even in French, one would say j'aime le pain (the concept, the food) but je mange du pain because I'm only eating a part of all the bread in the world.
Not sure about the correction that was proposed to you, but the Italian sentence says: A mia figlia piacciono le mele. That is 'my daughter likes apples". That's a singular, one daughter. 'My daughters like apples' is therefore incorrect.