Every person is different. If your sugars are stable, that's great. But there's a lot of things that makes your sugars unstable: stress, anxiety, sickness, not sleeping well, kind of food you eat, how much exercise you do, menstrual cycle, your own attitude.
Many many things influence rise and fall of blood sugar in Type 1's. Primary, of course, are the insulin injected and the carbs consumed and the relationship between the two. (If not enough insulin to cover the carbs, numbers go up too high, if too much insulin, numbers go low). But if the person is still in their honeymoon phase then their own body still produces some insulin which further affects blood sugar. However there are other things that can affect blood sugar including illness, stress and even more subtle things for some such as temperature, hot showers, etc.