If your tax returns are connected (doing them together) the software is probably applying the medical deduction to the person with the lowest income.  If 3% is only $300, your wife is probably not paying any income tax anyway.  Medical deduction is a non-refundable tax credit.  If you are not paying tax, you get no refund.  Same thing for you.  If you are able to claim the spousal deduction, among others, you may not be paying any tax either, in which case, no change to the return.  It doesn't matter how much in medical you add.

If you show tax owing, and can make use of a medical deduction, you may have to start new unconnected returns so you can apply the medical where you want.  Be careful not to exceed deductions based on family income.