There are two artists known simply as 'Christina':

[1] Norwegian singer Christina Undhjem. She first came to fame with Danish band You Know Who in 1995. Two years later she released her own solo album entitled Watching You.

[2] Welsh vocalist Christina Booth, best known for her work with Welsh progressive rock band Magenta, with whom she's recorded 5 albums to date. She released her debut solo album, Broken Lives & Bleeding Hearts in May 2010.