I'm not surprised by Chantal and I don't think anyone needs to feel that bad for Shannon. But it is more proof of Chantal's inhumanity, and worth discussing, even if it's not surprising. I think certain things Chantal does hits a nerve more than others and it depends on the person.
Look at this on paper. You have a best friend for 30 years. They try to include you in social events and important milestones even when everyone else hates you. They defend you even when you're making an ass of yourself. They try to help you get out of an abusive relationship-- maybe not in the most elegant way, but they are basically the only person on earth not obligated by blood who is actually trying to help you. For that, you rage out on them in public and drag them through the muck.
Then their dad dies, so you send them a steak house certificate. A few months later they attempt suicide and end up in a mental ward, so you block them for being a drain.
Most reasonable people, even if they were angry with their friend and haven't spoken to them in months, would show the smallest bit of humanity when their friend has a family loss or a mental health emergency. This is the only person besides Pee and her mom that has tried to be there for Chantal. She sucks, but she is quite literally the best and last female friend Chantal will ever have. Her KOCs arent friends. Every single day Chantal finds a new way to ensure her own future suffering. Amazing.
I've known some real assholes in my life, but some of them manage to scrounge up loyalty for at least one other person, even if it's another asshole. I think that's what has some people so triggered by this.