What's the best way to reduce cat dander?

Shave the cat?

I think that constant cleaning drasticallly reduces it, which keeps it from building up in all kinds of small places.

Good ventilation helps as well. A spotless house with open windows will work wonders, as well as vacuming things like couches, etc. that harbor dander.

We Did shave the cat!! HAHA! I think the dander is still here.

Shaving the cat and cleaning (especially with a hepa filter) certainly helps. But if your friend is highly allergic, I’d recommend a benadryl (or antihistimine of choice) before arriving. The allergy is related to proteins in the saliva of the cat and if your cat lives in the house, there is no way to completely eliminate them.