Her feet was hinted on the Jump Fiesta Trailer, and now, on the latest issue of Weekly Shonen Jump, it is confirmed that Yuna will appear on Dissidia 012, and yup, she will summon monsters!
In the scan, she has the ability to control two Aeons (the name of the summoned monsters on FFX) at the same time. The magazine has a screenshot that shows Yuna controlling Shiva and Ixion for simultaneous attacks. She is also said to summon King Bahamut in the game.
Her EX Burst is somewhat translated to as, Sending Off to the Spirit World, this attack makes Yuna call all of her Aeons for a consecutive set of attacks!
Sources: ffchaoticcosmos, Siliconera