I'm not able to help you but I did want to put my two cents in and maybe offer up a couple suggestions.
I wished that tiktok would have been eliminated in the US when it was mentioned by our last president.
That app is a child predator's paradise!! I know this to be a fact because I am a member of law enforcement (LE).
I realize that your daughter is smart enough to unblock her friends if you were to go into her phone and put a block on them. Maybe that won't be the right approach, but what about talking to those kids parents?
Eventually this problem you're having is going to progress and get worse. Instead of her friends sending her these videos, the child predator could.
If it gets to that point, you've got to take the phone away from your child and hand the phone over to your local LE agency. They might have the resources to track the predator down. If not, they need to contact the investigators at the Rupert Police Department in Rupert, ID.
We have an investigator, on our force here in Rupert, that has successfully tracked down and arrested these predator's from within Idaho and several of the surrounding states.
I'm too new on here to know whether or not I can attach urls to our local newspapers and media or I would.
My best suggestion is to put a stop to it quickly, like you're trying to do already.
Keep up the fight!!