Earlier on, we saw a picture of a family who appeared to be welcoming their mother home from prison. This picture seems to have come from the same school of humor. We're sure people's grandparents do occasionally go to rehab, but they don't tend to get welcomed home from it with an over-the-top airport sign.
The only thing that makes us wonder whether this might be real is the little bit of detail on the bottom right, which suggests grandma has been sober for seventeen days. That seems oddly specific.