In an unaltered 1795, Angelique would still have been strangled by Barnabas as the first victim of the curse, buried in the woods, and risen as a restless and vengeful spirit with sights soon set on Josette. Her first appearance was as a disembodied head, though Vicki's trial showed us she was capable of appearing human for a time and vanishing again at will. But by the end of 1795, her spirit was only able to strike out from the portrait-- the same one that will travel to 1968; this is what lead me to believe that by the time Bathia Mapes shows up at Collinwood, Angelique has already been consigned to hell. Before Vicki went back in time, who knows how long Angelique would have languished there, which is why I'm intrigued by your theory, mscbryk.
But in my heart, I don't believe there's an explanation for her existence as a human during 1840, just as there isn't one for either the surge in her powers (she's capable of lifting the curse, which the much more powerful Angelique of 1897 couldn't pull off) or the amazingly sudden change in her personality during that time period.