What is incumbent upon one who vowed to fast two consecutive months upon success, and then regretted her vow?

A vow of recompense is disliked, but it must be fulfilled if its condition is met. Therefore, you must fast two consecutive months unless there is a legitimate excuse. If the time is limited, the missed Ramadan fasts take precedence. If there is ample time for both, then the missed fasts are still more deserving of priority.