Is it obligatory to make up for a fast by someone who introduced water into her vagina while bathing during a Ramadan day due to obsessive-compulsive disorder, and should the make-up fast be postponed due to obsessive-compulsive disorder?

You are not required to make up for those days, and your fear and dislike of obsessive thoughts are a sign of faith, so pay no attention to them. If your feeling of water entering does not reach the level of certainty, then you don't have to make up for it. Some scholars have even stated that fasting is not invalidated by something entering one of the two orifices. If you were unaware of the ruling, your fasting is valid. We do not advise you to delay making up for what you owe from Ramadan.