Hi again Lynne
Generally people were admitted to the Workhouse if they were too poor or too ill to care for themselves and their families. If this is in fact your Elizabeth in the Workhouse, it might be that her husband has died or deserted her and she is without an income and therefore unable to care for herself and any children they may have had together. Or she might have become ill and have no family with the means to care for her. I am assuming that you have already tried to trace both James and Elizabeth in Census after their marriage??
Cheers
Karenlee