What should a wife do who discovered her husband's infidelity via phone, with pictures and conversations, especially since they have a daughter? Should she ask for a divorce, or continue living with him after his denial of the incident?

You can supplicate to Allah to improve your husband's situation. What your husband did does not affect the marital bond, but if he is committing grave sins and persists in them, this permits you to seek a divorce. However, it is not advisable to seek a divorce; rather, it is better to be patient and advise him, out of concern for your daughter, and not to neglect marital rights.