We published a paper last year when I was a student. I submitted this paper’s abstract to a conference this year after I graduated and I did not ask my coauthors about this. Now this abstract get accept and will be presented at the conference. One of the coauthor who is my previous supervisor sent an email to me saying this is ethical problems that I should not present without her permission. She looks very mad. I wonder if she is true that I need all co authors permission to present our published paper at conference. I planned to cite our paper and mentioned this is a teamwork when presenting at the conference. What should I do?
In my view, there are at least two distinct categories of conferences, though they may not be explicitly labeled as such and I'm sure there are examples that fall somewhere in the middle.
The first type are those where people gather from all over (though the geographical extent can vary) to present and learn about new work to their field (however broadly/narrowly defined). These are often regularly scheduled affairs (e.g., annually), may require that content presented be fully original (though in my field the expectation is that it is not published at submission, not necessarily that it is not published by presentation), and typically have some sort of review process (ranging from a basic check "yes this is science", to a full detailed peer-review).
For that type of conference, you submit work with coauthors, so you need permission from all coauthors to submit and present. Just like for papers submitted to journals, it's considered rude or outright unethical to submit to multiple conferences like this.
The second type of conference is usually more local, and more often consists of a collection of invited presenters. They are likely to be ad hoc, or have shifting topics. The attendees may be almost all people who live/study nearby, though speakers may come from further away.
For this type of conference, people present as individuals and credit their coauthors (and cite their own published work and work of others) throughout their talk. The presentations are really no different from other types of invited talks (including interview talks), the only thing that makes anything different is that they are grouped together. Sometimes these talks (just like other invited talks) have original content or in-progress work - I would get permission before using anything that hasn't been shown before - but otherwise they are expected to be on things already presented elsewhere. If all the figures, concepts, etc. presented are already published, then in principle there is nothing that would even prevent someone else from giving a talk about your work, so there's no need to get explicit permission. Implicit permission is already granted by having the work published.
I'm not certain which category you fall into. Your coauthor seems to think it's the first type, as does your submission method: you sent in an abstract for approval, and it was accepted. If you had other people listed as coauthors on that abstract, you need their permission to submit. On the other hand, it seems like this is work that's already published. If the conference expected work to be novel, then you've possibly also broken the submission rules (even if it was accepted, it's possible they didn't realize it was published if you didn't say so).
In life sciences, chemistry, biology and related fields you publish and peer review papers in journals, you don't publish in conferences. Giving a talk about a published paper or displaying a poster about it at a conference would not require asking permission from any of your coauthors. The work is already published, the author list is fixed and the authors are acknowledged in your talk or your poster.
For unpublished work you should make sure everyone is on board with your general strategy around how much you want to present to the outside before it is published. That doesn't necessarily mean asking for permission from everyone every time you show parts of it at a conference, but your collaborators should know and agree with the choice to show this material in general.
In these fields it would usually be assumed that e.g. PhD students show part of the work in progress in posters at conferences they attend. If there are specific concerns about sensitive information, e.g. if you plan to patent something or if there is the perception of a high chance of getting scooped, you have to be more careful about what you want to show. But apart from that the general expectation is that scientist will show their work in progress at conferences.
There are obviously very large difference between fields here, this answer does not apply to any field where conferences are a way of publishing your results and an alternative or replacement for journals.