If I've got the wording right here, Tarn basically gets to treat the two ships Shara has locked as ones that he has locked, forcing them to reroll dice, while also having his own lock on Norra to let her reroll the blank that Finn adds.
That would be awesome but it looks like it doesn't work that way. Shara's ability only effects a ship when it is attacking. Tarn can consider those targets locked by him while he is attacking but that really doesn't help at all with M9-G8 since he can't consider those ships locked when they are attacking.
Edited by WWHSD