Who is she? A Jedi Master who fought during the Clone Wars. One of the first Jedi to go up against General Grievous and managed to survived, albeit heavily injured. Aayla was intelligent and mischievous, but ended up being killed by her Clone Troopers on Felucia because of Order 66.
Why include her? The way the films handle Aayla may have left a bad taste in Star Wars fans’ mouths, and this would be a good way of making up for that. Her skill in infiltration and stealth would make her deadly on the battlefield and could quickly end up turning the tide of battle for the rebels.