She says, "Hello to you, too, sphere hunters. I am Marnela of the Cactuar Nation. It does not surprise me that you are startled." (By the way, she's smiling.)
Marnela is a Cactuar and the leader of the Cactuar Nation in Final Fantasy X-2. She communicates with the Gullwings through an Al Bhed child named Benzo in order to protect the nation from Angra Mainyu. Her name in the Cactuar language means "Grandma".
Marnela was first encountered during the mission at Bikanel Desert. Nhadala, leader of the Al Bhed excavation camp, asks the Gullwings to represent their camp with the help of their Cactuar interpreter Benzo. Marnela had wished to meet with the camp, but Nhadala and her team were too busy and asked the Gullwings to meet her in their stead.
When Yuna and the team arrive, they are surprised to learn Marnela is a giant cactus. Marnela explains through Benzo that when a Cactuar matures, they root themselves deep into the ground and become cacti. The Cactuar Nation she leads have watched over the desert "since the dawn of time". She tells of a fiend once sealed by her ancestors that has recently awakened, and asks the Gullwings to find the Ten Gatekeepers that can summon the Great Haboob, a magical barrier, against the impending attack.
Fiends begin to appear around the desert, and encroach into Cactuar Nation. When they began their invasion on the Nation, the Gullwings help Marnela to protect the area. Marnela shocks them by firing laser beams towards the fiends; she is able to fend them off for the Gullwings giving them extra time to find the Gatekeepers, but she uses all of her strength and dies. At the end of the quest Benzo reveals that a cactus sprout had appeared in Marnela's stead, ready to grow as a new Marnela.