In Shadow and Bone, it is revealed that when she was tested as a child for signs of her Grisha ability, she knew that if she was found to be a Grisha, she would be taken away from her best friend, Mal. When she realized this, albeit subconsciously, she hid her power so that she could stay with him at Keramzin. She did not consciously realize that she had been suppressing her power until she saved Mal's life in the Shadow Fold.
Because she was the only one of her kind, the Darkling felt a particular connection to her, as he was also the only one of with his power, and believed he needed her to balance out his darkness.
However, at the end of Ruin and Rising, after using all three of Morozova's Amplifiers, her power transcends herself through said amplifiers and is taken from her. Instead, the Sun Summoning power is bestowed upon random people around the country, perhaps further. Alina loses her powers as a Grisha, passing it onto the others in her stead and it is these new Sun Summoners who go on to destroy the Shadow Fold. It is currently unknown what becomes of these newly created Grisha and their gifts.