My father left when I was 2 months old and when I was 19 I called him (idiot me). He was great. He told me that he felt really guilty for leaving me and not visiting me. We had alot of fun together. No-one could say a bad word against him, not my mum, not the people who had been there all my life helping raise me, feed me, clothe me etc. I staunchly defended him - he was my dad and I was proud of him and he was the greatest.
Unfortunately it didn't take long for his true colours to shine through. Only as an adult (I know 19 is adult, but its young adult) have I been able to assess the situation for what it is - no more rose coloured glasses, no more being bought - just the plain old truth. I can't explain the pain I went through during this process, but I got through it and now have time for only the people who have been good to me throughout my life, and he is not one of them.
Unless your stepdaughter is very unintelligent I believe that one day she will wake up like I did. As an adult she will be able to see things more objectively and pay tribute and respect to those who deserve it. But I don't think it will happen in the teenage years. I hope this gives you some hope.