First, I am so sorry for you. Judy is now at peace. We will pray for you and your family.
The camper, what you are describing has indications of a roof leak that water followed the corner of the camper down to the floor where it then is trapped by the waterproof membrane and then rotted that area. The roof substrate
holding the rubber on is also deteriorated.
There may also be a corner molding leak. The gutter spout on the camper can blast the corner molding seal and water can get in that was too as well as towing in the rain. And there are other areas such as clearance lights and even a window seal. Or some part of all of them.
The good news, this is very fixable. The way your camper is made this can be repaired from the outside. Yes, it is best to fix this "first" from the outside in. I would suggest to not try to start this repair from the inside as it can damage the wall board bad enough it has to be replaced. And depending on how bad the damage is, the wall board may be gone too band still the outside would need to come apart to fix the rotted wood. Taking siding off your 2004 is not that hard to to.
Now the harder part, cost. While the camper is repairable, hiring this repair out to do a "complete" repair is very labor intensive. It just takes lots of hours of work. And those hours at whatever shop rate they have can go into $1,000's real fast. If you are looking for a stop gap fix, or a fast patch that can last a year or so and then sell the camper as is, that can be a cheaper option to try slow down the leak. This does nothing to fix the damage, but will at least slow it down. You need to work through, do I want to keep the camper or not.
If you have the "time", have common woodworking tools and have done home wood projects of most any kind, then those skills can be used to fix the camper. We can help with the "how to".
I do not want to scare you, but help show what you are to expect. There are some really ugly pictures of what that type of leak looks like inside the walls and roof.
First, I suggest buying a moisture meter so you can scan the entire camper to see how big the problem is. There may be more than one area, just now you found the right rear corner. See this thread to help with the meter. Suggest scanning the entire camper and making sketches of the camper with the moisture readings. When you are done, then you can see how big the water issue is and how many of them you have. This is a $40 US tool that can help with the decision of how good or bad this problem is. http://www.sunlineclub.com/forums/f7...per-17613.html
Here are some rebuild project pics that can show you what you could be up against.
This camper had a rear corner leak and a rubber band spongy roof feeling. It is a slide camper but is a very good example. This camper wanted to be kept so we did a total roof job. Yours may not have to go that far but it shows the walls and how it all comes apart and put back together.
This post is a non slide camper and a 2004. It too has back wall issues but I did not make it to totally fixing that yet. The front is fixed but the post is not yet finished. Again this can show how to take it apart.
And here is one that is in worse shape than yours. It had a roof leak that was only caulked (patched with no repair) and then years went by and the rotted wood let go at the roof line and water just kept coming in. I only show this to help with how the rear of the camper comes apart. I have not made it to putting it back together yet. http://www.sunlineclub.com/forums/f7...avy-17684.html
Hope this helps and we are her to support you as we can.