If it is everyone's responsibility then everyone should do it means, if it is everyone's responsibility, then everyone should do the training.
It isn't. Hence not everyone does the training.
I've been on many safeguarding courses and the crux of it is, there are so many signs that you are not qualified to diagnose, so if something feels off, then refer, to the safeguarding officer, as previously mentioned.
One course didn't even give that advice, they had to email at the end to say 'oh we meant to give you this vital piece of information'.
It is a box ticking exercise that organisations use when they 'learn lessons'. If you volunteer to hand out coffee you should not be in the dock for not flagging an issue if something happens when the powers that be send the shit rolling down the hill saying 'well, they went on the training'. That's not good enough IMHO.
She isn't a councillor, or therapist. She hands people drinks. If she sees a bruise, refer it. If she sees or hears anything out of the norm, refer it. That's all anyone needs to do.