she will go shopping next sunday if she won't be busy麻烦帮看一下,这句话哪错了,

问题描述:

she will go shopping next sunday if she won't be busy
麻烦帮看一下,这句话哪错了,

改为:she will go shopping next sunday if she isn't busy.
主句用将来时,从句用一般现在时.
我是英语教师,不明可再问.