My advice might not perform a great help but from my own feelings I only can warn to handle this problem and the involved people sensitively! I can only speak of myself but the natural healthy way of taking action to negative stimuli, if it is required for you to decide, proves the idiom to be true: honesty is the best policy (in the vast majority of cases...); unless no lifes are harmed like being asked by a killer or things would happen that would generally be regarded as grave (for example an agent is discovered operating in a criminal gang or a war conflict with bad authorities could evolve) but normally I try my best to prevent such situations to appear at all. Personally, I feel self-interested inhonesty as a bad character. If no one would want to damage other people and act selfish there would be no need for it. Inhonesty in non-critical situations for living beings leads to suboptimal, expansive and non-transparent living and working together and to the bad unfair world we are living in. Imagine the pointlessness of being asked for feedback, if someone can't be honest with it? If you don't want to hear hontest answers of any sort, don't ask for it! But being honest still must be destinguished from bad criticism and bad expression. If your character is not even good enough to honestly reveal it, you've not earned your friends anyways. No one is being helped with not being honest to someone. It doesn't help solving the actual problem unless your aim of life is not about making the world a good place for all but a place of your very own benefit (for example a good reputation from "friends" or other people) or for your exploit, which resembles more the sort of nihilistic answers to life.
Regarding ignorance:
Ignorance might hurt some people more than telling them the direct truth (including me and that's my experience). To me it feels like being not worth or good enough human being, because of the way I am, to being told the truth from someone. For example: Do you know the feeling when not getting replied again by a bad personnel management? The actual drawback on people's feelings is dependent on the psychological setting and therefore it's different for different people however, generally if you don't know someone well enough to make choose your action, still don't forget to consider the case, it could hurt the person's feelings or even worse destroy a person's long-term self esteem and it is even said, the girl from the post suffers from depression. In the worst case you make people more prone to depression or strengthen it, depending on the emotional lability and weakness of the person. It might be that her toxic character and the way she communicates is already influenced by her psychological situation to ease and distract from her own psychological problems, by her environment (not teaching/educating her better) and her experience.
And maybe the strategy works out fine for a lot of people, so you should know the person well enough if you choose the approach of active alienation.
Maybe they can call me insane but from my empirical view, being ignored or not honest enough in conversions also can reinforce the reason and desire of conversation and contact. Generally, if you know that close contact will have no overwhelming positive long-term effect for both parties and you need to stop things, you need to remove the reason for the interaction and not (only) the interaction itself. If you have problems being unwillingly contacted by someone, maybe it helps to find out the reason felt by the person who is looking for contact and clear it.
But let's reason from the empirical perspective why we need another answer to the question than alienation: Problems don't get solved by ignoring them, neither in mathematics nor in society. It's like the infant logic: what I don't see doesn't exist. While it might be true for your own consciousness you can't know for sure how other people feel about it. While some people project the behaviour from others back to others, some may project it to themselves.
Even if it doesn't seem so for some people, ignorance can be perceived as an explicit negative action spawning another reaction to it since you can't not communicate, -> Paul Watzlawick (except in some exceptional states of consciousness, for example if people don't know about each other or have the physical ability to change the communication state like passed out people). Otherwise if you force other people in a situation where they "need" the contact to cut it off instead, there is a serious potential of damage and it maybe reinforces their personal problems.
If you want a person to change you should help her/him as long as it is obviously safe for your life conditions to try it. Explain the person the problem and what he/she could do against it.
