Hi Mohini, Welcome to JustAnswer. I am a licensed veterinarian and I'll do my best to help you and Coco. In my experience Coco's reaction to the sedative can occasionally happen, but I don't know that it is common in white cats. I'm very glad to hear that Coco's twitching has stopped, but understand your concern because she is now quiet and she does also have future procedures that will require a general anesthesia for her dental and sedatives for dematting.
Perhaps this time Coco received a different sedative? There are several different sedatives that can be used, so I would definitely find out which she had this time and have her record clearly flagged that she had a reaction and in the future needs a different sedative.
Before Coco's dental procedure (or maybe even sooner if she is not perking up) she should have a blood profile and a thorough exam to make sure the anesthesia and dental safe for her. I almost always also place an IV catheter for fluid treatment during anesthesia. This will keep her well hydrated and helps the body to eliminate the anesthesia quickly after the procedure.
Of course I would also avoid having the same sedative given.