She had taken some pictures (that were saved into the phone memory) which I had to transfer to my laptop.
I went to File Manager, and copied the Images into the memory card (as it was previously on the phone memory). Then transferred them into the laptop. Deleted the copied images in the memory card through the laptop.
My mom called this morning and said all her sms-es (hundreds of them) have gone missing! She asked if I had deleted it.
I don't remember deleting it at all, only the images.
But I did make a change,
File Manager > "save files to memory card" instead of the originally-set "save files to phone memory."