If she uses the coupon, she will pay 2*0.5 = $<<2*0.5=1>>1 for each 4oz package.
Thus, she will pay 4 + 2*1 = $<<4+2*1=6>>6 in total for the 8oz package and the two 4oz packages she needs to reach 16 oz of butter when using the coupon.
Therefore, the lowest amount she can pay is $6, as this is cheaper than the $7 price for a 16 oz package.
#### 6