I assumed the false memories would start with Henry, that moment she gave him up–but we have no idea what else is changed or not.
Perhaps her false memory is that Neal sent her the 20k as he intended (but that August stole) so that’s how she managed with baby Henry years ago–or even that she wasn’t in jail (the second time did we see the handcuffs?), and the father was a fireman she met working at a diner as she had lied to Henry back in True North in season 1.
At some point, she will recover all her memories and these false ones will integrate in. I love the idea that her moments with Henry are really Regina’s memories with Henry reconfigured. I assume the magic just had a way of filling in the details that would be necessary for the desired effect to occur.
“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass