A dopplganger witch sister and a originals love

what if Elena had a half sister
Lilith Griffins is the daughter of Isobel and Alaric Saltzman
and the half sister of Elena Gilbert .
Isabel had Lilith when she was mortal but never told until she tells Elena when she about to kill herself but compels her to forget for 13 years and then tells Alaric when she remembered again

The originals are living happily after ten years when a witch put a curses on Hope (Klaus daughter) that can only be cured by the blood of a human Petrova descendants but they go to Mystic Falls when they arrive Elena remembers what Isobel told her and they go looking for the child.

Lilith Griffins live in a Foster house when she runs away to find her biological parents

what nobody know is that the first doppelganger had a sister who magic was past down from each doppelgangers sister.

when Lilith mets Elijah there is and a powerful
spark.