I forgot the title name HELP PLEASE!

Please I don’t remember the title and didn’t save it! It was about the ML (female ) who was suddenly transported into another world where she was a noble with a family consisting of her father and I think two brothers. She tries to convince them that she the real deal. I remember she a was found near a lake ? And the last thing I read from the story was that the real girl/sister sent the oldest brother (I think) a letter by some bird saying sorry for her disappearance and how she ended up in love with a commoner, and saying sorry she won’t come back. I know it’s a lot I cannot remember the title. thank you ..