We need a solution which is compatible with Islamic laws regarding the following case: a thirty year old…

We need a solution which is compatible with Islamic laws regarding the following case: a thirty year old woman of our relatives has three children, two sons and a daughter. She waits for her husband, in their house, who has been missing for ten years and he is with a mental disorder. Now, her mother wants to get her married to another man. Is it permissible for her to marry without divorce from her missing husband due to the aforementioned reason?