Are we doing the right thing?

Hi, I am new here. Not new to being a parent but definitely new to being a parent of a teenager. Me and my husband are in our late 20s and long story short, we were just granted guardianship of a 15-year-old. She is one of the sweetest kids in the world when we first met her, she fit right into our lives and it's been an absolute joy having her around. Anyway, when we were given guardianship, DCFS made it very clear that she is to not speak to her "ex-girlfriend" AKA a woman in her 20's who is clearly a predator, we made it very clear to our 15 year old that she must not speak with her because 1. it's illegal but also 2. morally it's wrong and quite frankly disgusting. Her "girlfriend" is not a good person, obviously. The 15 year old is extremely naïve and I can already tell she thinks she knows everything, just like I did when I was 15 years old. We decided to put a phone number on her phone but when she was living with her grandparents she wasn't allowed to have a phone period, but their reasoning is because they are old boomers and they don't believe in technology. I have been using the bark app on that phone, but because it is a Moto 5G it won't allow me to have hardly any access. I knew something was going on because she stopped spending as much time with us and she stopped using her phone around me. Plus my husband swears he can hear her ex's voice over the phone. I'm very good with technology and anything on her phone or on the iPad I can figure out an under five minutes, she's been living with us for almost 2 months and she has been messaging the "girlfriend". Anyway our plan is she is grounded for a month. She is losing the iPad for a month and she's only allowed to use her cell phone if she is sitting next to me or my husband she's not allowed to bring it to her room and she's not allowed to bring it to school. She's also not allowed to use any of her friends cell phones for the next month. I plan to buy an actual bark phone. We were going to get her an iPhone just like mine, but she has betrayed our trust and until she earns our trust back, I do not feel comfortable giving her an iPhone. we are also going to go to the courthouse and put in a no contact order. A police officer gave me this little blue card. He said I just have to bring it to the courthouse and it's no issue. Do y'all think that we are handling this well? I think she thinks just because we treat her well and we show her respect that we're not going to enforce rules. Yes I am kind to her but I don't put up with being lied to, especially for weeks. I won't tolerate it. I am heartbroken and disappointed in her. We love her more than anything, and before you ask this ex-girlfriend who is a woman in her 20s in the past has had access to inappropriate photos of the 15-year-old. So yes, she is a creep. She is a predator and she has taken advantage of the 15-year-old before.💔💔💔