There can sometimes be small gaps in the north west corner, when two walls meet. In these cases sometimes you can throw a teleporter pyramid to get through. Getting through accidentally is very rare, though, and I don't recall if there is a gap there (sounds familiar, so I'd guess so). A glitch with the character position could get through a wall even without a gap.
I don't recall this being reported before for the female warrior, or a difference between characters such as this.
How frequently does this happen? Does it make a difference if you remove the character's equipment?
If you start a new game with another female warrior, does this happen running around Aleroth?
Try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
With the GOG version, in the (optional) Galaxy client, select the game in the left column, then click on the More button, and in the Manage menu select 'Verify / Repair'.
