Lying really has nothing to do with different rules at different houses. It's about character. Children lie sometimes. Some children lie often. I used to lie often and frequently about everything and nothing at all. Mostly I lied for two reasons, I loved a tall tale and to get my way.
Continue to be consistent in your discipline and rewards systems in the house. Quiet as it is kept since she is 8 she knows there will be different rules in different places. She is testing boundaries. It is good for her to have a place in her life where she learns to be disciplined and it is equally good for her to have a place where she can be free and easy.
Sports, school, summer camp, activities and social groups all have their own set of rules and guidelines for code of conduct that may be very different from her two homes but she has learned to manage them too. NEVER reward bad behavior or slack off in the expectations of her because she has comply of suffer the consequences of not doing what you have asked while at the same time perhaps suggesting the rewards for complying with the requests will be helpful too. It's a delicate balancing act.
In 10 short years she will be an adult and need to know how to do things like cook, clean, and manage her time. The home is the first place she learns these things. You being her step mom can help her learn these valuable skills along the way because it does take a village.