Kids can overpass the security to use devices the way they want to.
So, no, I would not get her wifi enabled phone.
With her stealing, I would not reward her with the very things she tries to steal. If she gains legal possession of them, then I would require her to earn it by working a real job out in the real world. Let her learn the true cost of things by flipping burgers, washing dishes, or checking out customers.
My oldest son attended New Technologies high school, and the school issues laptops instead of textbooks. He over ridded the software keeping them from using them inappropriately and was caught using the school computer to watch inappropriate content. He would also talk to other kids and adults who were bad influences on him, and he was also a bad influence on them. He would not stop and had horrible tantrums when I would try to make him. One of his tantrums ended with the police being called and him going to a behavioral health hospital for 9 days. That freaked him out, so he settled down some after that, but not as much as I wanted.
Technology is all around us and it seems there is no turning the hands back. The only option is to teach kids appropriate guidelines and set firm boundaries. When this doesn't work, and it didn't for mine, then the only option is to take it from them. The school helped with this by requiring him to turn his laptop in every Friday afternoon leave it at school over the weekend. He could pick it back up on Monday mornings. This meant he could not do homework or use it to study or collaborate with other students on group projects except for Monday-Thursday. They would check his computer to see what he had been doing with it, and if history had been deleted, then they were going to be keeping it every day and assigning him after school study hall for homework time with supervision. This continued for the rest of the entire school year.
The stealing, safety concerns, and illegality involved in her behaviors would concern me the most. It is illegal for minors to watch inappropriate content. It's hard to enforce though. If the people she is luring to talk with sexually are minors, it is illegal also.
I would seek out psychiatric help and maybe even hospitalization or some kind of facility for her. If there is an incident in which the authorities get involved, don't try to shield her from it. When we as parents can't help our kids, then we need those who can to do so. It doesn't mean you are a bad parent. It just means that the behaviors your kid is having is more than you are able to deal with. Protecting her from consequences and mandated help is hurting her rather then helping her. You can advocate for her within that system, but don't try to keep her out of it. Insist on her receiving rehabilitation.
This is one of the hardest things for a parent to go through. I have been one of those moms who called the cops on my own kid. It is heart breaking, but when that's the only resource you have left, it can be very effective. Sometimes we as parents have to get out of the way, so that those with more authority can deal with stuff. And you would be amazed at how much grace and strength God offers during those times.