I don't know, and can't imagine, what cruel things this friend has said about your DGC but I could see a situation when there is a bit of banter - and that can escalate from funny to cruel in seconds - where perhaps you said something slightly derogatory about one - maybe referred to scruffiness or tardiness - which your friend mistook for playfulness without recognising the signals.
you can say things but she has absolutely no right to
I am very suspicious of repartee and banter.
I know someone who thinks it's funny to poke fun at everyone he meets . Mostly he gets away with it but occasionally it gets taken the wrong way and it can be upsetting.
Last weekend, in Rutland, the first statue in Britain of the late Elizabeth II was unveiled.