My eight year old stepdaughter is really pushing her limits around here?

Here in the last 6 months my stepdaughter has been acting out we have tried everything that was implemented on us as kids TIME OUT TAKING ALL THE THINGS SHE ENJOYS OUT OF HER ROOM HER MOM HAS ED HER A FEW TIMES WE'VE SAT DOWN AND TALKED TO HER NUMEROUS TIMES ABOUT IS THERE SOMETHING WRONG THAT SHE NEEDS TO TELL US all in all here's the deal she is constantly lying about things sneaking food and drinks into her bedroom throwing her food under the table when she don't want and lies about it in story form telling us how good it is and she goes through phases of really bad grades one week and amazing grades the next she has been acting out towards her two cats at times too me as her step father have not ed her some people tell me I should to let her know I mean buisness but not to sure I'm comfortable with that I do punish her alot of the time and stick with it her biological father isn't in them picture barely at all so I try my hardest to man up and be there for 110% of the time I now have my very own biological child on the way and want it to be a joyful experience for all of us but I don't want her to influence her sister or lie to us about anything with the baby I myself was raised my grandparents and had a very full enjoyful life with them till the day they died and I want the same for her as anyone would for their children she has a councilor that will be seeing her soon we had a consultation with her family doctor to see what he thought and he said he was very happy to see we cared enough to notice the issues and referred us to counselor so is that good idea I'm reaching out asking serious questions here so if you have some stupid little quote please take it somewhere else these are people looking for serious answers and advice thank for your input and have a good day