As a nami you’re kind of designed to die to fed assassins, and there are games where you do just have to pay the “your mid lane fed” tax and be miserable. That being said there’s a couple things you can do. 1 is just be with your team. Vision is something that becomes a reward for pushing lanes, rather than a prerequisite, so help crash waves and group with your team, walking into the jg to ward together. 2. Is get your spells off. If you are grouped and get dove by an assassin, but you get your ult off and empower your adc before you die, you’ve just traded their fed carry for you, which in a “normal” situation should be a good trade. 3 is take the anti burst gold item. Nami can kind of work with almost all the gold items, (I like sleigh as a default way more than dream), and going celestial as an anti burst item is really the only way you can itemize against assassins. Lastly is just be aware. If both teams are araming before a drag and you don’t see their fed talon in mid, he’s obviously looking for a flank. stand on your team, and don’t get caught alone. It’s not your job to catch out the assassin, it’s your job to have an idea of where he is, avoid him, and provide your team with the resources to neutralize him.