"if I could convince my sister she did something"
OMG. How diabolical! But yes, I've heard about psychologists implanting false memories, and whatnot. Of course a person can be tricked into a belief if they were young enough when the thing was supposed to have happened. I have memories myself that I question, because I've seen photographs of myself as a child, and I wonder, do I remember the thing or the photo of the thing? :0
"Don't all parents lie to their children in some way or another?"
Santa says yes. :)
This is an indicator. A parent could apply various stories to that image that will be carried along too making it even more plausible.
This is one thing we were never lied to about. I was told not to tell other children though. Socially programmed instead ;)