When multiple students share items with you, it can quickly become unorganized in the Explore tab of your ePortfolio. It is not possible to delete items that have been shared with you.
Therefore, after giving feedback, ask if the student wants to stop sharing the item. If the student does not do this, you can choose to ignore the student in your ePortfolio. You will then no longer see any shared items from this student. You can also reverse this setting.