Idea for Margarette Bubbles:
When she appears without her lazy eye, and you call her out on her appearance, there could be more things that happens. One, her eye becomes deviated right in front of you and the doppelganger says "my eye's always been like that." Or two, she tells you she had surgery to get her lazy eye fixed, which could actually be the truth– you'd need to verify it somehow though.
People having their moles removed could also be a possibility.