I have a slightly different view from others about an outright social media ban. I will caveat this by saying my teens (one 18 and one 14) have not had issues with self-harm or suicide ideation, however, my eldest does have some history of mental health distress, and likely has undiagnosed autism coupled with OCD and my youngest is going through an ADHD assessment.
Firstly - forget the vaping. Tell her you don't like it, you think it's bad for her and you wish she would quit, but as long as she doesn't do it in front of you, in the house, in front of her siblings or get into trouble at school, its her health and money she is throwing down the drain!
I smoked when I was her age (eventually quit in my early 20's). My parents didn't and hated it. They would occasionally have a bit of a dig about it - but as long as they didn't catch me 'in the act', it just became something we didn't talk about. Even as an adult living in my own house, I never smoked in front of them or my little brother!
Re: the social media. My eldest wasn't bothered by it until she was about 16 when she got an instagram and snapchat account. Youngest had her instagram account last year. Neither use TikTok but do get exposed to it via cross platform shares and eldest DDs boyfriend watches it a lot.
I don't 'police' what they are watching directly - but do keep an eye on it indirectly (obviously not so much with the eldest now of course).
The way I do this is by showing an interest in what they are watching - we sometimes sit and watch reels together - when eldest was 15 / 16 and before she got her own account, one of her favourite things to do in the evening was to sit with me for 30 minutes before bed watching reels - usually about cats, funny situations or things related to theatre shows and TV shows we liked.
If something a bit off came up it meant we had opportunity to talk about it. It also gave me an opportunity to explain algorithms and how damaging some things could be and encourage her to let me know if something came up that wasn't right.
I also try to gently nudge their algorythms by sharing things I have found funny or interesting and getting them to share stuff back with me - it helps to move it away from some of the more damaging stuff.
Obviously if you feel more comfortable with an outright ban or it is recommended by her therapist then that is completely your call - however, I would be worried she would just watch in secret anyway. She will be 16 soon, so beyond completely removing her phone / stringent parental controls, you will start to lose that control anyway.
Personally I find it better to open up the relationship with social media so it becomes something you share because I don't think it is something that can be avoided for teens in this day and age.