She was the luckiest person in the world, and she was eternally grateful to the Drysdale family for everything they had done and put her through, as she would not be here walking towards him if it hadn't been for them. And because of her gratitude, she showed mercy by not killing Gwen and by leaving the bodies of the two men intact, even though she had only drained them.

They were going to die anyway, so there was no reason for them to keep that blood inside them. So, it wasn't much of a sacrifice for her to take their blood to repay everything she had done for them...