Can my old supervisor publish my work without my say so
Formally, no.
Your former supervisor seems to be trying to coerce you into working on something you do not want to work on. &quot;Getting this done shouldn't be too taxing&quot; sounds like the kind of argument of a person who does not want to engage with your argument, but merely wants to get their way. You can choose to give her what she wants, but you can also choose to not do this. If the work is getting you down, why not just stop? You can tell your supervisor &quot;no&quot; in a polite way.
Your supervisor cannot publish your work without your input or consent. If your supervisor submits your work under her own name (without you as a co-author), this is a violation of academic integrity, and if you can show that she took things from your thesis, you can force a retraction of the paper. If she submits the work with you as a co-author (as she should), then you retain control: all authors must consent to the paper being submitted. A good venue will send all co-authors an email notifying them of the paper submission, and if you object to the submission, it should be removed from the reviewing process. It would be very unwise of your supervisor to try to sneak your work into a publication without your consent: if this ends up with a retraction, this will be bad for her reputation.
You worked for this person during your PhD, but that is now water under the bridge. You no longer work for this person, so you don't owe her anything. If she is wise, she will leave it at that. If she is unwise enough to try to pull a fast one on you, you have ways to fix the fallout. So, you should be fine.