Is the marriage of a woman who was forced into it and dislikes her husband, and then secretly married another man, Islamically valid?

What the questioner did by marrying before divorce and the completion of the waiting period is a grave abomination, because she is still under the legal bond of her first husband. She must repent to Allah Almighty and cut off her relationship with the man she secretly married. Neither dreams nor justifications permit what she has done.

She has the right to seek annulment from her first husband before a judge if she is not content with him. If her marriage is annulled and her waiting period ends, then she may marry with a guardian and witnesses.