IGN - Linkle was almost in Link's family, fans responsible for Linkle's in-game appearance

Coming from an IGN interview with Eiji Aonuma...

Hyrule Warriors developer Koei Tecmo originally pitched Linkle as a member of Link’s family

Eiji Aonuma: “Koei Tecmo first proposed the Linkle character as Link's little sister for the Wii U version of Hyrule Warriors. However, we felt this conflicted with the concept of Aryll from The Legend of Zelda: The Wind Waker, the only character we had ever had appear as Link's sister, so we decided not to include that version. In Hyrule Warriors Legends, though, the proposal was to include Linkle not as Link's sister, but as a girl with heroic aspirations. This was a totally new and unique background for the franchise, and we thought she would add to the game's diversity, so we decided to include her in this game.”

Zelda fans played a big role in Nintendo reconsidering Linkle

Aonuma: “We had a great response from fans, especially outside of Japan, who saw Linkle in the Hyrule Warriors premium-box booklet and wanted her to be included in the game. Seeing that reaction, Hayashi-san and I talked it over and decided that we would definitely like to include her in the next title. I'm really glad we got the chance to do that with Hyrule Warriors Legends.”