Hi Emily,
The company you work for has HR policies.? And those are known to protect folk like you.? If so that means HR will be on your side.
Your supervisor, however, believes that those rules don't apply, and by not being overtly offensive, and a residual drip-drip of covert offensiveness (creating an emotional abuse script of "not good enough, not fast enough, watch out when I'm around"), is hoping to drive you away.
This is not appropriate behaviour from a supervisor - if there is a performance issue, it needs to be taken up with HR, but my feelings are that there isn't an issue, and they know it.
So, what to do - document, document, document. Every time something bad is said. Once you've done that for a week or two, lay an ultimatum - decist or it's going to HR.
If they don't decist, then take the log of things said, to HR, and explain that this is making working very stressful, and that you suspect other coworkers may be feeling the same way.
You have rights Emily. Lots of them. If there is a citizens advice bureau, use it. If you have support from therapy, use it. If you have a workers support line (fairly common), then use it.
Time to pull on the big girl pants and fight for you - you've already done that once already, so you can do this hon.
(Hugs) because this is a stressful and anxious position to be in. We are here for you.
Rowan.
