world gets deleted

when me and my sister got back on our computers ( on different days and different worlds) both of our worlds were gone. we did not delete them and they are both worlds that we were last on when we played.My sister was on a few hours ago and when she got back on minecraft her world had gotten deleted. mine happened a few days or about a week ago. I decided to report it now since its not just my computer. She and i may have just stayed on the world and closed our laptops or something but they are worlds we have had for weeks.
i wanted to prevent it from happening to other MC users
thanks.

steps to reproduce,

We have no memory erasing programs on our laptops.

The only other person able to get on our laptops is our mom, she only does this to help us with schoolwork or problems on our pc. but our entire family was gone during the time it happened, and when we all came back i went on my pc and the world on my pc was gone, and this same thing happened to my sister yesterday.

UPDATE:
this problem is now resolved. my sister found out that her world was on the bottom of her list and it had no name and was creative (when it used to be survival and it had a name on it) and said she played it " long ago " when she had last played it 3 days ago ( the time i posted this bug. ) the same thing is with my world that had the same thing happened if you have this problem simply look at the bottom of your worlds list and you will find a world that's creative with no name even if you have just played it recently before you get the bug.