[...is that an honest question? How does she even explain this?]

It's not just a 'thank you' like they're magic words or something. It's... a matter of respect. In our world, that's a really big deal. The way that you said it was like you were giving the Brigade all the credit and only putting Sokka's name in there as an afterthought so he wouldn't get mad. That's almost worse than not putting his name in at all. That's why it would have to be from you and not just a sign or something - to show that you acknowledge what he did.