I mentioned to my wife that there are some very intelligent people who say that free will is an illusion. She responded by blowing a very loud rasberry while waving her arms up and down, then said "get them to analyse that".
So there is a challenge.
What built in instinct and logic was responsible in my wife's brain to initiate this behaviour?
Warning - she may have some more challenging tests to come!
She'll have to do better than that I'm afraid; all that anecdote illustrates is that she, like you, simply has not understood the issue. Many people take free will to mean that we can do things that are out of character, that is a trivial understanding of the issue and if that is what you want to call free will then fair enough.
However if you or your wife want to develop a deeper understanding of the issue then take this challenge - try to want something that you don't want. For example, assuming you are heterosexual, use your will to make yourself want to be gay. I don't think you can honestly do this, any more than you can use your will to make yourself believe something that you don't believe.
These observations illustrate a deep truth about all life that you simply haven't yet understood - that we are fashioned by nature, we do not fashion it. We start out life gifted a shuffled pack of parental genes over which we have no control, this sets the broad parameters for what we can become, and subsequently what we actually become depends on the experiences that come our way; thus your wife to date has become someone who would quite likely choose blowing a raspberry as a way of expressing indignation in a comic manner.
Our will expresses our personal nature but we cannot control the fundamental laws of nature, we are subject to them, we are manifestations of them. If you think you can be free of your nature by dint of willpower, then take my test and try to want to be gay this afternoon; let us know how you got on.