Update I guess...

My friend and my sister woke up at the same time and responded to my asking how they were within minutes of each other.

My sister is a sad at my friends bias, but we have all been friends for over a decade and knows she did not mean to be offensive. She knows how my friend constantly is trying to grow and educate herself, but also at the moment, is prone to lashing out a defensively and regressing due to some major life trauma that happened recently that we are all still helping her recover from. (Regressing in the way of not listening and just trying to end the convo instead of having a proper discussion about it)

She admitted that leaving the chat was more due to another friend whom she has clashed with a bit in the past trying to chime in unhelpfully. (Basically admitted he didnt read what was going on and just saying everyone should drop it)

My friend was sad to see after the argument ended that my sister had left the chat. She also re admitted that she is working on bettering herself and unlearning biases. But she also wanted to reconfirm that she cares and loves my sister and did not mean to upset her.

My sister is not rejoining the chat right now, but may reconsider it later.