Step-Daughter is being made fun of at school for having no contact with her biological father, How do I explain to her that she has an amazing dad even though there is no biological relation?

My boyfriend and I have been together for almost four years and have a 7 month old son together. Prior to my boyfriend and I being together, he was engaged to a woman we will call ‘K’ and they have a 7 year old son and an 8 year old daughter together. The daughter is a product of infidelity, knows that my SO is not her biological dad, but loves him to the moon and back. My SO cut her umbilical cord when she was an infant, has always been the father figure in her life, etc,. And while she has never seen a problem with her biological father being mainly absent in her life (as she is proud to have my SO as her father), Recently K has revealed to us that she has recently had troubles with classmates.K explained to me that my step-daughter came home from school this past week having a full on melt down about not getting to see her biological father. When K asked why stepdaughter was so upset, step daughter revealed to her that a girl in her class was teasing her -when they were talking about their own parents- about the fact that she “doesn’t get to see her biological father”, and how “it’s weird that she is excited to see someone who isn’t even her ‘real dad’”. K explained to my step daughter that there was nothing wrong with her father(my SO) and that she should appreciate how much he does for her and how good of a father he is to her and her brothers. Stepdaughter apparently continued to cry for a while but then dropped the issue and went on with her day.Of course, hearing this, I’m furious that someone else’s child would say such a hurtful thing to my stepdaughter regarding her father. K also tells me that she had later on confronted the girls mother, explaining the situation and saying how her daughter (girl who was teasing stepdaughter) has to be held accountable for her actions. The woman basically replied back with excuses for her daughter, and saying that she believed her daughter shouldn’t be held accountable for what she says because she’s just a child etc,. And the situation is pretty much over.I suppose my question is; Is there any way we can make her feel more secure in the situation she is in? She LOVES my SO to the end of the world and back, calls him ‘dad’, and we try our best to let her know that she is SO very important and loved by the both of us. I just want to know if there’s anything else we can do or if anyone else has experienced a similar situation? My SO is pretty sad that she had a meltdown over this in the first place but glad that K seemed to calm her down a bit.Thanks in advance! via /r/Parenting http://ift.tt/2DAZilN