How to child-proof the outside of my iPhone?

I'm visiting a baby tomorrow who is a little older than one and I have downloaded a few apps for her. I'm terribly afraid that she will drool all over my case and phone and ruin it. I have already set up in-app guidance to use. I do not have any time to buy another case, like an otter box or Fischer-price baby case. Already I have a knock off otter box from 5- below, and it works well, but it's just not water/drool/chew proof. Any ideas?

Be with her when she has it and keep an eye on it.

Ziploc bag?