Should I keep my last employer off my resume?

You should put your last employer on your resume along with all duties you have accomplished during your time there. Despite how your supervisor behavior was towards you, I am sure you had other superiors and co-workers who will confirm your duties and professionalism as well.

Leaving that position off, employers (present and future) will question you about that gap in your employment.

Good Luck.

It may be possible. If the job isn't too critical - like if you didn't really work there too long and you can think of a reason to fill the gap, then don't even include it. Another option, just so you stay honest is to include that work in your work history but don't list anyone there as work reference.

They can. It doesn't mean they will. How long dis you work there? Is that your only potential bad reference? I can't say based on the little information provided.

If in the opinion of the manager, you were not performing to the minimum level required, then she is compelled to say that. If you think it is personal, then you should say the reason why there was friction between her and you.

If it would leave a significant gap in your work history, and you can tactfully explain why you were terminated, I'd put it down anyway. Appearing to have been unemployed long term will hurt you more than leaving a job on bad terms. They aren't going to call the manager for a reference unless you specifically list her as one. They just call to confirm that you worked there when you said you did, she's not really supposed to say anything more about you at all.

Yes, that is exactly what will be done. It is employers helping employers.