Re: How do you safely keep your recovery phrase written on paper?
I didn't told her about it to avoid more argument because she wouldn't still understand what it is.
You don't have to explain her everything, just that piece of paper contains the sort of password that you need to access your bitcoin. If that is not enough, show her the price of Bitcoin. 
I would like to know how others keep these secret phrases if the people in your house are not really knowledgeable in crypto.
My parents know that I am into crypto but they don't have any knowledge about it and they never created wallet/sent bitcoin or anything similar. That didn't stop me though from storing a copy of my cold storage seed phrase in their house as I explained them its a fail-safe in case something happens to my wallet and/or other seed phrase copies.