Telling a former supervisor you don't want to publish
Keep it short and sweet:

Dear [her name],
Thanks for the reminder about our project. I thought about it some more, and for personal reasons I won’t be able to continue with the work. Since you have all the data I suggest that you pursue publication by yourself or with other collaborators. And, if it matters, I do not care very much about the issue of coauthorship, so whatever you end up deciding about who should be a named coauthor of the paper once it’s finished is fine with me.
Regards,
Gerilk

An important point is that, since you’re worried she will try to pressure or guilt-trip you, you should not apologize for or explain your decision. Manipulative people are expert at using every sign of guilt or embarrassment to pressure people relentlessly until they get what they want from you. I can almost guarantee it from experience: if you give her a reason — any reason — she will find some counter-argument to make that reason look invalid or insufficient, and will repeat this as many times as necessary with any additional details you add to your explanation, until you give in. Do not give her an opening to do this. A firm “no” with no explanation is the only approach that works with this type of person.
Good luck!
Edit: there’s been an extensive discussion in the comments about whether the email should mention the subject of authorship. To clarify, I don’t think it matters very much if you mention it or not. I included that part since, first, it seems factually true based on what you said that you don’t care about authorship; and second, letting the former supervisor know this eliminates one possible pressure point she will surely try to use to keep pressuring and annoying you in the hope of getting you to change your mind.
But if you prefer not to mention this, that’s pretty much just as good and won’t particularly affect the outcome.