Arwen, sterbliche Königin

If the target of Arwen's second ability is illegal as it tries to resolve, the ability does nothing. You won't get to put any counters on Arwen.

You remove the indestructible counter from Arwen as a cost to activate its second ability. If Arwen already received 2 damage earlier in the turn, it will be destroyed due to having lethal damage before you get to put a +1/+1 counter on it.