I think Kang Min Ki killer her sister & Ha Do Yoon helped. When they showed close up of the bloody sword, the colors of the clothes looks like what he was wearing.
I think whatever wrong someone did in their past life/lives, they'll have to deal w/ karma in the next life. Ha Do Yoon did something really bad toward Seo Ha so he has to make up for it in this life?
Here's my wild theory... Kang Min Ki was in love w/ Ban Ji Eum. He had her sister killed to set Seo Ha up. Ha Do Yoon was the one that shot her w/ the arrow
The way she's acting will definitely get her killed