If When She Loved Me is one of Abi's choices, that's the one that will be on piano in my opinion. For better or worse, the judges have been really encouraging Abi to get off the piano, so she will almost certainly attempting to work the stage on one of her songs.
Hopefully, whatever song choice Abi had landed on has enough for a vocal showcase that is closer to Bring Me To Life than My Songs Know What You Did In The Dark.