Just an idea for consideration, there is a brush on product for vehicles that is used in place of spray-on Rhino Liner. Called Hercu-liner, it is durable and waterproof. Once cured, it should be inert.

You could put some plastic sheeting down, then plywood over your subfloor and over some (or all) of the sheetrock in the room, possibly even seal the gaps with a thin bead of caulk so that the Herculiner didn't bleed through, and then apply the herculiner over that, for a waterproof room.

If you install the extra plywood, if/when the time comes to change that room back from an animal room, you could easily remove the plywood, and have normal sheetrock and subflooring without having to replace it all. I don't know how messy the snake is, but I'm thinking that over the sheetrock, I'd run the 4x8 sheet longways, covering the lower 4' of the wall, if you don't think you'd need any covering the whole wall.

The herculiner comes in a bunch of different colors, so you could choose something that really offsets her coloring, or looks really natural, oh, the possibilities are endless!!!