A lady sent me a message ,to which I replied. She also replied back. All the messages are gone but her original one. I didnt delete anything and if she did it wouldnt delete mine,would it?

Did you accidentally delete them? Check both your inbox and sent :D

It doesn't matter what she does with her's, your's will stay there unless you delete them :D:D:D

The only way someones PMs will disappear, is if Admin totally bans them/their topics/comments and he/she includes the PM's too.