Its a battle for sure and the older she gets id think it'll get worse. When BM allows things yoi dont then you are the bad guy

Child's age? Custody schedule? Is your DH a decent parent? These are all factors.

Some apples fall away from the tree, but most don't. Kids tend to be very loyal towards their mothers, so there is a good chance her mother's influence will be more powerful than her father's, and most definitely, yours.

You've been Sm to the little child for five years , and she is now seven. It's just going to get harder from here out.

You can't control Mom nor what happens at Mom's house. All you and Dad can do is control how things are at your house. You have rules and guidelines in place for SD and she follows them (so far) at your house. So you are teaching her the 'right' routines/behavior expectations et. Best you can do.

Unless the father is willing to chance going for additional custody time and successfully win, this is what it is. 

Bedtime, brushing hair, eating habits. Of course, all things of concern. However unless Mom is a passed out druggie, physically abusing the child odds are not great to get much done about it. 

You keep showing the child routine and healthy, be the best influence on her you and Dad can be during the times you have her. 

How often do you have your Skids? The BM in my life is also a terrible mother. She is more concerned that Skids like her and think she is a cool mom than she is about parenting. Kid has a bad grade in class? Clearly it's the teacher, so change his teacher. Kids want to play inappropriate video games? Give in and then tell DH he's meddling when he objects - even if it's in your parenting plan that the kids are not allowed to play inappropriate video games (added by BM herself when she wanted to appear to be a good mom). Kids don't want to go to DH's house because they'd rather hang out with their friends? Demand a mediation to change the agreement, so kids spend less than EOWE with DH. I could go on...BM also regularly complains when Skids are with me (an adult, who can drive a car and take people to the hospital if necessary), but then regularly leaves Skids with her SS who is 16, but does not have a license and according to SKids stays in his room with the door closed. Skids have also learned to have temper tantrums to get what they want, because that's what BM does. They are also convinced that the world is out to get them, because BM is convinced of that. For example, whenever they have bad grades, it's not that they didn't hand in their homework or that they don't pay attention in class, it's that the teacher "is mean". 

We only have SKids EOWE, so there's not much we can do to correct for all of BM's bad influence, but we do try to set clear expectations. Of course, DH is not always good at holding those expectations because whenever he does try to parent, Skids will call mom to cry and say they want to come home and then BM will text and tell DH that the kids don't feel comfortable around him and she is going to come by to pick them up early. 

I've had to step back from a lot of things, including education. I can't manage around the fact that BM is always telling Skids that the teachers expect too much of them and it's not their fault they have Fs or Ds in middle school. They still know that I value education and hard work and they know I will help them if they need help, but that's all I can do as a stepmom. It's really difficult sometimes and it often makes me want to leave the house every time they are with us, but I'm trying to reach a place where I have disengaged enough that I don't feel too invested, while also not disengaging entirely, becuase I know that would impact my marriage. 

How often do you see SD?
Do you have 50/50, FT or are you an every other weekend stepmom?
The time you spend with your SD will impact on the how effective you can be with her.

Her mom doesn't care, what is her father doing about this?
Your profile says this is going on for around 5 years.
What makes you think you can change this now?