What you are looking for is CombatAnalysis.
However functionality of that plugin in LOTRO is not as wide as you might expect if you used such tools in other games; it can track your characters Damage Done, DPS, Healing Done, Healing Received, and events like stuns/mezzes etc; but it cannot track Threat, will have trouble tracking damage absorb shields you put on other players. Also what can be tracked can be tracked for your character only, not other group members.
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