As a temporary measure, they might try raising the side opposite the slide with boards or "Legos" to try and get the water to run away from the RV. I had a small Arctic Fox trailer that leaked water into one corner of the LR, turned out there was a metal channel trim piece at the bottom of the slide and rain water would run inside it especially if the RV was slightly tilted up on the slide side. Sealing the inside of the channel fixed the problem.
2004.5 GMC SLT CCLB, Ride Rites, Turbo brake, EFI Live
2012 Arctic Fox 29 5T 5th Airborne, B&W, Prodigy
Papillon navigators Lily, Buddy and Willow