What’s an appropriate age for kids to start having privacy when bathing?

My boyfriend and I have two daughters (each from previous relationships). His daughter (she’s 8 turning 9) lives with her mom and visits us weekly. My daughter loves with us and visits her dad weekly as well. When bathing my daughter (she’s 6) her dad and I give her privacy in the bathroom as well as changing in and out of her clothes. The only time we’ll come in is when she needs help with shampooing her hair. When my boyfriend bathes his daughter she tends to ask him for help a lot when changing & bathing. At home she’s totally capable of doing that herself just fine but when she’s with us it’s different. I’ve mentioned to him that she’s at an age now where she should have more privacy when it comes to baths here, she doesn’t want to do it alone. I don’t want to over step because I’m not her bio mother and I would like some advice or tips on how to go about the situation or if I should just leave it at that.