Child who cheats

Hi,
With all respect that doesn't necessarily means she is cheating.....  She might be afraid of your reaction.  I believe she is still not sure in her new place and tries to find her way (what to do and what not to do).  It is highly recommended that you built her self esteem.....  she is only 13, a very critical age....  please leave behind all what you know (and were told) about her, try to build trust and openess between you, teach her to communicate and respect each other, make her grow to be a good possitive woman....  No offence please but I feel you have a "fix idea" about her.... better give her a good chance, lots of love, and please please please don't be too strict to her.....  I remember that you are not her parents but you have now full responsibility. 
Best regards,

Bipolor she needs help. Abused or abandoned...why did the parents give her up?? They need to help her..not toss her to you.

Your posting is too short of details that are necessary for a good response. Was she the only child of her parents? Does she have siblings? What corrective measures did her parents take? Was she evaluated by a child psychologist? Was she ever punished? At what age did she come to you? How does she relate now to her parents?