Did Kaori know that Arima loved her? Did Kaori know that Arima loved her? From the letter she gave to Arima, she confessed everything and even gave that photograph, but at the same time, she told him to throw it away if he wanted to. This according to me suggests that she didn't know if Arima loved her. If she knew about Arima's feelings, she wouldn't have said it to him. Is there any strong evidence whether Kaori knew about Arima's feelings in the Manga/Anime?
I've only watched the anime (and a few months ago at that) but truth be told, I'm of the opinion that she did know that Arima had feelings for her. Take what I'm about to say with a grain of salt though as I do think that Kaori's true goal at the end was to get Arima to love himself somehow by whatever means she could. I don't think her true intention really was to get him to fall in love with her either but become a part of his life that would would galvanize his restoration. 

Here are my thoughts:

Throughout the series, Kaori shows immense respect towards Arima's skills having admitted at some point later in the series that he was a source of inspiration for her. As a result she seems overwhelmingly distraught at the state of disrepair that Arima has fallen into. She initially enters his life by the first performances together and using Watari. 

As this goes on its easy to see by everyone in the series that Arima has formed a dependency towards her (especially Tsubaki), and whether or not these are romantic, Kaori seems to realize this or even if she doesn't the scale of meddling and pushing Arima to strive towards reclaiming some former glory increases. Unfortunately Kaori is doomed, and then realizes that all her effort to push him to revitalize him is at stake and gives him her final wishes etc in an effort to convince him to move on with his life after her. I think this acknowledgement of dependency and her trying to help him move on from her as a result is key to the idea that she knows he loves her. 

I know I'm making Kaori seem manipulative (or unknowingly manipulative) and maybe I'm putting too much confidence in what she's capable of doing but at the least that's how I interpret it. As with the shows name, she lied. Kaori told Aroma, Watari, Tsubaki, and everyone else, that she loved Watari. By telling everyone this it was known as a fact. But then you realize she loves Arima instead. Resulting in," Your Lie in April," because she lied in the month of April by using Watari.