Advice!?! With Stepdaughter💜???

Thank you for checking my story out, But I warn you it may be long. I really need some serious advice about what to do..

Here's my dilemma...

My SO's daughter just turned 11 in February and I look at her like she's my stepdaughter, I knew her since she was 4years old we have what I thought was a great relationship. I always take her out buy her stuff do as much as I can to show her I really care about her.. Her dad works 6days a week so I'm home with our toddler, I initiate her visits and different activities that we do. It's been like the past few years. I really enjoy being with her.

Her mom is honestly a great mom But works ALOT and leaves her with her older sister who's 22... Who's Bf is ALWAYS staying the night over their house. So she gets exposed to a lot more now days.. I'll be blunt here...They are a bit.. "hood" to say.. So is her block and the surrounding area😦

Here's "THE " issue...

She recently got an iPhone a few months back for her Bday, she also started going to drill team and hanging out with some of the older and other girls from her school. She came over this week for easter break and left her phone charging in me and my SO's room, so at 3am she starts getting all these Instagram, KIK and flipgram,notifications..😒..pause.. I didn't even know 10-12year old were up that late!

What would you have done?!?

Sooo yes, I looked in her phone to see who it was, and it was a group feed about her and her other friends jumping some other girl.!😮But I also came to realize and find out she curses ALOT and the girls talk about inappropriate stuff.. her friends get dick pic's of older guys in their school when they are hard in their boxer's/briefs. My Sd now says how she wants a boyfriend and that she wants to go out with this boy is her class.. 😟😟 she also text's boys talking about if they like each other and her other friend told the boy about her..

Also

I seen how she doesn't want to come over here that much and says "she's mad AF" that she has to go to her dad's house!😭 and it's "Fucking boring over here".. she kind of talked some "shit" about me and my daughter sleeping in one afternoon only because I was up late with her having a fever and just being restless.. So she's dropping the "F bomb" all over the place to her friend about how "we're still fucking sleeping and "Oh now I wanna get the fuck up"..😔

My SO tried to go through her phone earlier that day and realized that she changed her password again..(I already knew it) BUT I didn't say anything because I didn't want him/her getting upset about it like she normally does when he checks her tablet. I found out her password later on that day.

My question is how do you handle a situation like this!?!?🙈🙉🙊😱

I want to talk to her about what she said to her friend and us being asleep that day along with a few other inappropriate things her friends talk about.. These girls are SERIOUSLY VULGAR!! Dick, stank ass pussy convos the works!!..

BUT I knw it's not going to go well.. I now notice that innocent role that she plays around us is just a front for how she really acts outside and at her friends house..

She's had the partial sex talk, and knows she's too young for boys and was told no boys period. No texting calling face timing ANYTHING.. BUT she does it anyways she even sent one a picture of her😕...

So at what age and point do kids have true "privacy" and when should parents not worry about this stuff?? I had a bad feeling with just how secretive she is.. Her mom doesn't check her phone and I knw she would be upset about this also.. Soooo

What do you do?!?

Would you have checked her phone?!?

Was I wrong!?!

Do you stay out if it and not say anything?!?

I don't want to look like a critic or an instigator.. Which normally happens😭 So should I do???