All you need is a good parental control with an essential function, screenshots of her phone😎. I had similar problem with my daughters and that was the only effectively working solution.
I use Ourpact on their Android phones that has this function, a few years ago I used Safelagoon with the same feature added (a little more expensive). Basically they take screenshots of your daughter's phone screen every few seconds while she opens an app and use it, while she touches or scroll the screen, these screenshots are saved online and you can see them by your phone at anytime. So it works on every app, no matter which one, snapchat included, including all the pictures, photos, websites, texts and messages. Magically you will see her messages, received and sent, even if they were quickly deleted.
I don't judge at all and I think nobody shoud do that, every situation is different and the effects of parents relly too much permissive about phones and socials are totally obvious nowadays. I used the same time limit of half an hour a day until 12yo, than 1hour a day (for all the apps except the ones for homework) until the late teen, 18 for my older one (with frequent exceptions on request), and yes, with the screen mirroring option enabled too. I'm not ashamed of that, call me control freak, I don't care, but it has never been like I was controlling her screenshots and messages everyday all the time, in the late teen it happened rarely and occasionally when I suspected something was wrong, when my daughters were younger it was a quick look everyday or every other day. I believe that knowing you can see what they are doing online is in itself a great effective deterrent to doing the wrong thing.
About trust, well she should trust you that it's all in her best interest and she should trust you wont check everything all the time, not more than what's necessary. Don't believe to the tale "all my peers don't have parental control", it's totally false and manipulative. They are minor, their phones monitored by the parents is always been an unavoidable condition for my daughters to have a phone.
I don't know if recently some cheaper alternative to Ourpact was released, with the same screenshots feature, that's not cheap but to me it's worth it. Please let me know if you find something cheaper equally valid.