Kirsten,
the comments of that previous owner of Lily shouldn't really bother you...each life is unpredictable and it's not in your hands what has happened to that other cat...maybe instead of accusing others the owner should give more care and concern to the remaining cat...
You've given Lily a wonderful home and she's loved not only by you, but also by Luna...they match perfectly and they just belong together...I don't think that the owner's cat would be any different if Lily would be still with him...
Just try not to be bothered too much by such comments, instead enjoy your life with your wonderful cats...