why did this macbook delete everything? can we get it back?

my friend was writing a paper in word, and had safari open. she had to force quit safari, and when she reopened it all her bookmarks were gone, along with word documents, pictures, songs, etc. also, her settings were back at default. something similar happened on her older desktop mac. is there any way she can get her stuff back? she cant find it anywhere, and why does this happen?