DO NOT get sucked in to her playing you off against her mum - the one that did the graft of raising her the last 12 years.
No it sounds like a perfectly NORMAL set up at home. Was the 'friend' a boyfriend? Someone that's led her astray in the past? You won't be able to answer that because you don't know her friends or her mum, you don't even really know her.
Honestly I think your other dsd and son aged 10 SHOULD be doing chores. Even if only lay table, clear table, empty dishwasher type things for 10 year old. And 12 (?) year old dsd can do most things. Everyone should contribute to the running of their home.
I bet if you spoke to her mum she's hardly bloody Cinderella! But a 15 year old looking to suck up to long lost dad and new stepmum will make out they are! My dd now 17 certainly at 15 was keeping her own room clean and tidy, her own laundry, dishes of an evening, cooking for us both once a week. In 3 years she is potentially going to be living alone and needing to look after herself either at uni or in a house share. Dd is now 17 working full time, does all I said before, cooks at the weekends, does all the hoovering, babysits for a friend at weekend for a few extra quid, gets any shopping I can't get online and cleans the bathroom once a week (there are parts I can't do/reach due to disability).
I don't have younger DC but it's also totally normal for them to look after younger siblings at that age and in a single parent household may be necessary due to work shifts etc. I'm the eldest of 3 and I certainly looked after younger siblings from the age of 14. I grew up in a genuinely abusive household. This was NOT abusive, most of my friends the same age did the same as do dds friends, her best friend is the eldest of 5 and does this.
Harry Enfields depiction of teenagehood is painfully accurate in some ways. Eg ask them to put their plate in dishwasher "it's not fair! I have to do EVERYTHING round here!!"
Be very mindful you're only getting ONE very BIASED version here.