It is a tiny photo for my old eyes. ;-)
What year is the Scamp
? Does it have a laminate type wall covering on the bathroom wall under the window?
I had the bathroom window on my Scamp
start to leak on a very rainy 4 day trip. By the time I got home the water had gotten between the Laminate/wall covering and the fiberglass outside shell. It did cause a small area of only about 4" x 2" to discolor as your photo shows due to the water getting behind the wall covering. When I took the window out to fix it I was able to see down a little bit between the wall covering and the fiberglass (only in the area that was discolored) enough to see that mold was not an issue. As I said that was in my own situation yours may be different. I on first finding the leak did attempt to cover it up as much as possible while still camping to prevent to much water from entering so I know it did not take a while lot of water to get between the bathroom liner and the fiberglass to cause such a stain on the wall. Due to the fiberglass shower pan it makes it hard to determine if there is any serious floor damage without removing the shower pan but as Donna suggests take a look under the trailer to see if the floor is stained - if it is that would be a pretty good indicator that a fair amount of water did get into the trailer.
In regards to the stains on the two walls that do not have a window on I would suggests its more likely they were caused by a leak in the rivet on the roof and not the window. Water leaking in via a roof rivet will travel between the roof and insulation and show up as a stain on the side wall rather than the roof. Did the owner replace the roof rivets as well?