young insecure girl -- Insecure teen (You say 'she' later on so you don't need to say girl)
who lost her boyfriend by an accident,-- When her boyfriend dies (Don't need to tell us by accident)
is sending -- Sends
a naked video to a strange men -- begins sexting random men (A bit more colloquial)
which is causing bullying attacks at school -- (This whole part should either be changed or used as the inciting incident) (Such as, When an insecure teen becomes the target of bulling after her sexting video goes viral)
she is moving- she moves
to a new town to build friendship (Transfers to a new school)
but the cyber attacks continue (but the cyber bullying continues)
and increase her depression. (Drop this, she needs a pro-active goal)
Hope that helps, good luck with this!