This D’var Torah was prepared and presented by my 4th grade daughter as part of an assignment for her class – she used the Midrash says as her guide to write it (I hope that you enjoy it as much as I do):
How did Serach know? Before Yoseph was niftar he told her this password that he learned from Yaakov. How did Serach live so long? Two weeks ago it says in the parsha that the brothers went up to Yaakov to tell him Yoseph was still alive and they brought Serach bas Asher to play her harp and sing Yoseph is alive in Egypt. Yaakov was so happy that he gave her a blessing that she should live forever.