Though it also said Mary was not inspired in a real person. But think about it - to paint a portrait of a person that looks so real someone might confuse it for an actual person/photo, Guertena must have put a lot of effort (aka his 'soul) into it. So maybe that's the reason why Mary is more alive than all the other paintings. As for Fake!Garry, I always took it that Ib was hallucinating due to the loss and the fact she didn't understand Garry had died. So she sees this mirage of him and refuses to go back home without him, so she follows him.