Most likely the pipes have a loose coupling if they're plastic, or a nail or screw has penetrated one of them.

If it's cast iron pipe, the wall of one may have corroded away.

A dishwasher setup can be extremely nasty. If you have a small leak, perhaps from an aged coupling or clamp, or from one of those ungodly cheap corrugated drain lines, it could build and build for a long time.

There's no way a pipe can be smelly unless something is growing on it or dripping down it. What are these pipes? Water supply? Electrical conduit? Waste? Plumbing vent? Dryer vent? Were these smelly pipes examined while the dishwasher was running a cycle, or the clothes washer?

A pipe won't smell bad by itself. The solution is at least one step further away than the stinky pipe. Is there mildew inside the wall? Does she have a dead critter?