You are right, Iptumu...I know little about the worth of oleander as an immune system builder...and even less about colitis.
But I do feel that there is always the chance that kids, or people who don't know anything about the plant, might be tempted to try it in some unsafe way, and be sorry they did.
Have you had successes with it? Any noticeable improvements?
The only thing I could guess would be useful for alleviating colitis would be very gentle treatment, a little of this and that, so as to restore strength to the area, a bit at a time.
Gentle exercise, starting with gentle flexing and stretching, even lying down, might help. Movement is always useful...it is the lymph system's only pump.
Add in gentle and full exhaling on the effort, to ensure that the following full breath will send oxygen directly to the muscles just flexed.
That's probably where I would start.
I wish you well.