The story is not transmigration or reincarnation but about the ultimate 'prophecy' that the wet nurse of the prince had written as a story that is popular to commoners. That wet nurse is an employee of our very own MC.
The MC or Yulias only likes money (she caught it because of his family also love money), she does not care or perhaps only thinks money and that is the reason why she agreed to the Proposal of the Marquis because they are below them (Earl) but in truth, they are wealthier than them and that is the reason of the engagement. The Marquis' son, Lamore... how do I type this? Yup, he has a pit on his brain. He chose an ex-commoner that has only been expose to the society and trying-hard-to-be-aristocrat (Yuri?) than a pure bred young lady that is so damn wealthy and also wise and witty (namely Yulias) In short, he chose a copper instead of a gold. He is truly an idiot because their family are already declining and he wants to annul their engagement that cost a consolation fee in return.
When Yulias doesn't need him anymore (she doesn't need him at all anyway and only need his title for exporting goods) she and his father, schemed about her marriage that whoever cheats must pay the consolation fee. Yulias befriended the Prince and helps him to getaway with the girl that tries to be the heroine of the ultimate 'prophecy'. Fortunately, Yulias is the (more or less) owner of the 'prophecy' that is why she has the knowledge when will Yuri strikes.