I don't know the story with this woman-but I know that not everyone who uses a wheelchair for medical reasons is incapable of walking. Sometimes it's that you can walk-but it's very painful(or stressful to your body in a way that isn't healthy)to do so. So sometimes seeing someone standing from a wheelchair is less "I don't need the chair I'm just lazy" and more "I can do this one thing".
Some people in wheelchairs can walk, however the distance they can is very short so they use wheelchairs in cases like this, when they're out buying things.
You don't know her story.