This question already has an answer here:
In the End, Rose throws off the Heart of Ocean in the Sea.There are numerous theories trying to find out the real reason.
1).The fact that it didn’t belong to her anyways.So it would be unethical to keep it.
2)She was gonna die anyways
3)She threw it to complete a "Life Circle".Gave something to where it all began.
Any other strong reasoning why she let it go?
Edit: The other question is similar, but does not cover all possible reasons.I have mentioned the answer there in above bullet points