As far as I know and see from personal experience and what I heard from friends with IBD and from my gastroenterologist, there are two types: Those who have always been lactose intolerant from childhood on and those who developed lactose intolerance duet to inflammation especially in the small intestine. If I understand it correctly, it should only occur when the small intestine is affected, as the resorption capacity is decreased, same with fructose for some of us.
As I child I was not lactose intolerant, so it's unlikely that it will stay there forever. As the role of gut flora is not completely clear about lactose intolerance, there is not a certain advice to help with lactose intolerance apart from reducing the daily intake of lactose.
In fact, I have noticed an improvement of my lactose intolerance in the past few WEEKS, when I changed my diet again completely, slowly increasing the intake of sour milk products. Finally I'm now able to tolerate "normal" dairy, not the labeled lactose free products. Set yoghurt is now working, same with quark. I don't overdo it of course. I have never thought that this would be possible ever again, so I'm very thankful to my nutritionist. If she is right, a healthier gut flora, altered by foods and in the beginning also probiotics helps the small intestine to be able to get along with lactose again.
According to my nutritionist this is nothing surprising and a normal process. If you are not lactose intolerant from childhood on, it's very unlikely that it will persist for the rest of your life, especially when being in remission (unfortunately I'm still far away from remission, so I'm very surprised about that good outcome after such a short amount of time).