One of the safest means to have your bitcoin under your control is in using bitcoincore, but when things like this happened, then there must be something hidden and unexposed to you, who ever have access to your system aside your wife, who taught you about how to make use of bitcoincore, do you also browse the internet with that same system you used for your wallet, how do you safe keep your wallet private keys, all of these are means through which you could have been attacked without knowing as i guess.