Translation:The girl eats apples because she loves fruit.
They are both subordinating conjunctions and are used to explain the reason for what's happening in the main clause:
Jag gjorde det, därför att jag var tvungen. Jag gjorde det, eftersom jag var tvungen. I did it, because I had to.
The difference is that eftersom can be used in the beginning of the sentence as well, which därför att most often cannot:
Eftersom jag var tvungen, gjorde jag det. (Since I had to, I did.)
Both in Swedish and in English, we prefer to use frukt/fruit as a mass noun when talking about fruit seen as food. If you talk about them as single items of fruit, or different kinds of fruit, you could say frukter/fruits – 'Äpplen och päron är frukter' Apples and pears are fruits
In the sentence, it is said she eats apples. While i understand what you are saying (and it is certainly grammatically correct), I find it odd to then say "because she loves fruit" (and not fruits). It just sounds odd to me. I used fruits initially and was told it was wrong. I find it a bit harsh given the overall translation and meaning is still accurate