How about y/n being adopted by nat when she was rescued in a mission when she was a baby? Then after that she grows up and join the missions. But one day she and nat had a very bad argument like y/n saying that I wish you weren't my mom then nat snapping and telling her that she wasn't even her daughter anyway.
And they never talk again, but when they went to fight thanos(make her live) and then when thanos snapped his finger y/n started to disintergrate her last word being I'm sorry mom and I love you with last smile and then nat ran to hug y/n but she didn't make it so she shout out through her lungs