13 year old step daughter

Okay so my significant other has two girls age 13 n 10 with another woman...we've been together going on three years n it has definitely been a bumpy road with his ex...she has two girls n one boy who is not biologically his but he has raised since he was baby...so his ex told him about a month ago that she found dick pics n sexting messages in her iPad n phone...then once again she found more about sucking dick...we get the kids every weekend n the last time we had a very serious talk with her...so now every since then she doesn't want to come on weekends...she came like one day a couple weeks ago n we ended up taking her phone n iPad away for a few hours because she was not answering her dads calls n texts...Then I get this angry texts from the ex saying that she got grounded for not coming over..I immediately called her n told her the actual true story..she had nothing to say but that her daughter will not be coming over on weekends..well he has a court order stating he gets them every weekend...now would u guys go back to court stating the mother is not abiding...thing is yes she is 13 but she is still a child..I really think she just wants to be home alone on nights her mom works till 4 in the morning...recipe for teenage pregnancy I believe...what do u ladies think??