This happened to one of our homebuilders, people kept locking themselves out on a balcony of a model home.
The PPR Keyed entry levers have a pushbutton for locking. When the door opens, it may push back against a surface and inadvertently lock the mechanism. This might happen against a wall, and a door stop could prevent it. In other cases, a piece of furniture or a stair railing is in the direct path. That was the case for our builder, and we finally had to replace that lever with a passage function.
For this customer, the locking does not occur every time, so it may be a function of how hard the door is opened – it may not hit or hit hard enough to lock it every time. Check with her and see if this is possibly the cause.