Blackballing in Competitive Specialties?

There's someone in my cohort with extensive family connections and is an incredibly vindictive person. Every relationship ends with "betrayal" by the other person, whether that's a mentor, friend, colleague, their parents, etc. Essentially, doomed if you do know them, and doomed if you don't and they don't like your voice. Someone who chronically makes up story and lies, and gets away with it.

My concern personally, is that I was their mentor for a few years and of course, like every other relationship, ended in a slander campaign and anger that they can't exert control, and accuse me of gaslighting etc, just like everyone else they knew.

My concern now is that as I'm looking into a specialty considered high in the competition list, that this person may try to use their family connections to shut down these prospects. I'm the first in my community here, so a bit shaken. Thankfully, merit is not an issue, but there's much more to this than just merit and good character.