Advice Time

I am asking for your advice. I am presented with a problem that I am not sure how to handle. It is about S. She listens to me wonderfully all day, with her normal child mistakes and occasional warnings and time-outs. As soon as her parents come home, that is out the window and I am reaching my breaking point. It really has to do with the fact they don't discipline her AT ALL! For example, the other day S was sitting on the back cushion of the couch and was squishing it. Her mom told her to get off, but S didn't listen (as usual). The mother then pulled the cushion out from her and S just sat there and watched her. No telling her not to do it again. No time-out. Nothing. I discipline S. I feel that it is a very important. So all the things I tell her not to do, she does them THE SECOND her parents walk in the door. I tell her not to sit on the arm of the couch, she looks at her mom, then at me and stays there. I tell her not to go in the baby's seat (with its 30 lb. limit and she is 45 lbs.), she looks at mom and then does it. I tell her to get off the counter, so I pick her up so she can see, she kicks me so I put her down, then climbs up on the counter. All as soon as her parents get home. Making it even worse, S looks at me with the look of "Ha, ha, I won't get in trouble with my mom/dad even though they tell me not to do it too." And for the rest of the evening until I go upstairs, she is rude/whiny/crabby towards me. And her parents do nothing about it. They just let her get away with not listening and being rude to me. I won't put up with this complete disrespect towards me and don't think I should have to. And not only is it disrespectful towards me, it is towards her parents, S should not feel that she can do whatever she wants when they are around. But they let her get away with murder, so it is no wonder she feels that way. It is to the point that if she keeps being disrespectful to me, it is something that could make me reconsider my job because like I said, I am almost at my breaking point. I have already told S twice this week that she can not be like that with me. What I need advice on is should I talk to the parents about this? I think I should, however, how do I do it without telling them they need to discipline their child? That is not up to me to tell them. But the issue of her not listening to me and being rude goes hand in hand with the discipline issue, as does the issue of her thinking when they are home, she can do whatever she wants. I need to tell them I won't put up with her disrespect towards me, do I also tell them about the disrespect to them as well? And how do I do all this? So many questions... I really need some advice on this.