World deleted after minecraft update..no solution found!!!!!!

This problem has happened before. Not only to me and my siblings but to many people who play the game. When I launched minecraft for my little sister to play, it said the game needed an update so I pressed ok. After the update was done my little sister played on the map she had been working on for months. The world was at the top of the list. She loaded it and it wasn't recognizable. She was confused and frustrated saying this wasn't the same map and that all her hard work was deleted. She told me this happened to her multiple times but it has happened only after a minecraft update. I searched high and low for solutions on the internet, I've checked everywhere. I've seen people have had the same problem since 2012 but no one has a solution. I'm confused on how you guys haven't fixed it yet. It's been 5 years and mojang or 4j studios hasn't fixed the issue. I hope after seeing this you guys will fix it. Or give a solution to the problem. I've been contacting mojang and 4j studios and all they say is "here's a websight to submit your problem and we'll check it out" but what they mean is here's a websight you can submit your issue and we will never contact you back or ever give you an answer. I'm fed up with this situation just fix the dang problem....Thankyou