She said he was near death and in an effort to "prolong his life" she gave him some of her blood and "it all went wrong". According to Helen she "spent all the intervening years trying to undo that mistake." I think part of her wished or hoped she could safe him. He is not only the patient she lost, but the love her life she couldn't save.
Does she still care about him? Yeah I think part of her does. She cares for the man he used to be, the one she was engaged to 130 +/- years ago. It's possible they haven't seen each other since 1888 when she shot him in the alleyway. She had the embryo frozen for a 100 years and only brought Ashley to terms when she thought John was dead. She even said "forgive me John, after tainting her blood knowing it would cause him problems.