Nigeria will now meet hosts Germany in Sunday's final at Bielefeld, kick-off 2pm (BST). Colombia meet South Korea in the third-place play-off at the same venue, with an 11am (BST) start.
The only goal came from Joy Jegede's ball bouncing over keeper Paula Forero, coming back off the bar and giving Orji the gift of an open goal.
Desire Oparanozie had chances to double the lead, Colombia's came closest late on, also with an effort that came back off the bar, but with no-one to take advantage of Yorley Rincon's strike/
