If OL has Norra tl and Norra is firing at OL, can you use Shara's tl to reroll Norra's dice? Or do you have to have m9?

Sharas ability does say to treat it 'as their own' so I'm guessing you cannot and you would need m9 against OL

Is that correct?

Yes. It might be Shara's Target Lock, but Norra is the one trying to use it to modify her dice, which she cannot do if Omega has her locked.

M9-G8 works because his ship is considered the source of the modification, so the ship Omega has locked is not doing anything.

Makes sense. Man OL is frustrating lol

In such a situation, I would recommend Shara just use her target lock herself. Omega can't stop both ARCs.

As mentioned, it's important to consider who is the source of the modification. If it's the ship exchanging shots with OL, and OL has that ship locked, the mod can't be used.

The strangest cases in my opinion is when a ship allows another ship to do something. Like when a ship within R1 of Howlrunner attacks, Howl allows that ship to re-roll an attack dice, so the attacker is considered the source of the mod. Shara works the same way.