Trust!!

What is it to you when you think of the word TRUST. What does it mean? Truly what makes trust TRUST? I think that the word trust can be both an emotional and a logical act. Emotionally, it is where you expose your vulnerabilities to people, but believing they will not take advantage of your openness. I feel that my niece takes advantage of us every chance she gets. I try my damnedest to believe her, but she is always lying to me and dale. She is so good at lying she almost believes her own lies. What do you do when things happen that shouldn't happen and it effects the whole family. Now I feel logically, it is where you have assessed the probabilities of gain and loss, and that the person in question will behave in a predictable manner. I should not have to worry about a trust issue, but everyday it gets worse with my niece. I do not know what to do when she comes home and she lies through her teeth, I want to ripe her lips off her face. I am not happy with the lies, my whole family are liars and I have worked very hard to get myself not to lie
We feel we have no trust in this relationship. Dale and I are at our breaking point. I am not sure what you do when you are so close to something and this all happens.
Yesterday for instance, Dale dropped off my niece at school, 1 hour later I get a call telling me she is not at school but she has missed 1+ classes. So okay we waited to hear her end of the story. Well, her end of the story didn't make any sense to me, so I called the school this morning. They told me she skipped the whole day so I called the Principal of the school and told him to take disciplinary action for she had no excuse for not being in her classes. for dale and I, we have NO control of this girl for her father buys her BEER every weekend, but when I say I can't do this anymore and tell them to come and get her; they say NO she is unwanted around here and that she needs to stay with me and it is my responsibility and problem. What can I do. I have absolutely NO support from her parents. I am at my breaking point and I am so sick and tired of being sick and tired.
I try my damnedest to do the right thing for her but she has broken every means of trust and I have no clue of how to keep going on like this. My relationship with her is broken and I don't have a clue of how to fix it. I am at a loss for words.
Any Suggestions???