IPhone won't switch out of landscape mode during texting

My mother's iPhone won't switch out of landscape mode when she uses text messaging. Does anybody have any clue how to remedy this?

Did you lock it double press and you should see a little lock with a curved arrow

Press the home button really quick two times. A menu will come up at the bottom of the screen. Scroll to the left, and it will show the music icon, along with the play, rewind, and fast-forward icons. On the left of those will be an icon with a lock in the middle of a circular arrow. Tap this and it should say Portrait Orientation Locked. This will keep it out of landscape mode.