Oh gosh, this sounds difficult. Well done for getting a grievance lodged, it sounds like you’re doing everything correctly.

If you aren’t already then please keep note of times and dates and what happened, the Union already probably advised that.

I agree with Hope, bullies are usually insecure individuals, they are usually trying to bolster their own self esteem by belittling others.

I like Yaowen’s advice about creating distance by imagining she’s a mental patient. Years after I experienced bullying by a manager I realised how unstable this woman was, at the time all I could feel was the anxiety from the bullying. Creating a safe space by viewing her as someone to be pitied might be helpful.