Well, I say this a lot regarding HCDU, but one more time won't hurt.
The HCDU is a great starting point for finding possible conflicts, but there is a caveat. The program isn't guaranteed to find conflicts. What it does is find mods that change the same behaviors and, thus, have the potential to conflict. This doesn't necessarily mean they will. It's a great place to start though, because if you're having a problem, you can start by pulling out the mods the HDCU lists and hope it will solve things.
Conversely, if it doesn't list any potential conflicts, it doesn't mean they're aren't any. Just that it couldn't find any. At that point, the best course of action to take is to pull out all hacks/mods and hunt down the conflicting file the long way. Hopefully your cousin has them all in subfolders. It could also be a bad file hiding in the Downloads folder, which will mean hunting through its entire contents (for which I recommend the 50/50 method).