Question

if she leaves right now,she would get there on sunday这句话为什么不对

Answer 1

if she leaves right now,she WILL get there on sunday.
前面从句是一般现在时，后面的主句用一般将来时。would是过去时态，所以不适用。

Answer 2

英语一般是这样讲的。If she leaves right now, she would be able to get there on Sunday.
这句子明显是assumption的句子, 所以用will是错的。
是假设性的句子语法。