Responses
This happens quite often historically. Killing off any kin from the previous ruling figure assures the new family in power that there will not be any uprising in support of the previous family. It avoids unecessary future wars for the throne.
There might b supporters of the previous king in their kingdom who would rather serve the prince(ss?) instead of the new king. it can cause a rebellion
I know the king is a very bad person and I still dont get it why they need to kill our MC when she was a prince ... she hasn't done anything.....