From what I gather Kim treated Bianca more as a best friend than a daughter, which is a dangerous and unhealthy thing to do.
Hindsight is 20/20, there was a lot she could have done differently to prevent Bianca's death.
I think Kim should have taken away her phone or at least monitored her MUCH closer (as in not allowing her to use discord) as soon as the sex-tape fiasco happened.
Teenagers will be teenagers, you can't prevent everything but you can at least try.