Is the Dhuhr prayer obligatory for a woman who felt menstrual pain before Dhuhr but did not see blood until after the time for Dhuhr began and she delayed the prayer until just before the Asr time?

So long as the menstrual blood did not descend until a time when it is permissible to delay the Dhuhr prayer, then the prayer is no longer obligatory for you to make up, because the excusing impediment occurred during its time. For whoever catches one unit (rak'ah) of the prayer has caught its time. And if menstruation occurs when there remains from the time the duration of a complete rak'ah, then the impediment occurred in its time and the prayer is dropped. Repentance is obligatory for the negligence in hastening to perform the prayer at the beginning of its time if menstruation was feared, but making up the prayer is not obligatory.