The speaker is Geraldine, and she explains her distress in lines 71-99.  Geraldine says that yesterday morning she was kidnapped by "five warriors" whom she did not know.  She was tied to a white horse, and taken on a wild ride at great speed.  Exhausted from the ordeal, she was only half-conscious when they finally stopped, and the tallest warrior took her from her horse's back and laid her down beneath the tree where Christabel finds her.  The lady overheard the warriors say that they would be back, and she begs Christabel to help her.