In the manga and 2011 anime, Siper had a strong silent and stoic demeanor, while in the 1999 anime adaptation, she had more personality. She mentions preferring to shoot moving targets rather than stationary ones. She also was confident in being able to take out Gittarackur with a single shot.
Siper was a capable contestant, having reached the Third Phase of the Hunter Exam before being killed by Illumi. Since she passed the First Phase, she must have had above-average stamina. In both anime adaptations, Siper proved to be a capable marksman, and to be able to target Illumi without being discovered until she opened fire.
While it is not seen how she was killed in the manga, the two anime adaptations give her more screen time:
In the 1999 anime, she was shown to be capable of firing the cannons of a warship.
In the 1999 anime, Siper attempts to kill her target, Gittarackur, by sniping at him from a distance while he focuses on his own target, Goz. However, Goz takes the shot in the back and is mortally wounded. Gittarackur then kills her in retaliation for interfering with his battle.
In the 2011 anime, Siper is seen taking aim at Gittarackur, but is quickly killed when Gittarackur throws one of his needles through her scope that goes directly into her head.