If I share an item from my ePortfolio, will the reflection that has been linked to an item also be shared?
No, a reflection that has been linked to another item will not be send along with the item when you share it. This also goes the opposite way: if you share a reflection, the item that has been linked will not be shared.
If you share both the item and the linked reflection, they will both appear in the ePortfolio of the receiver, but they will not be linked. The item and the linked reflection will thus be two separate items after you share it.