Is Maggie representing Mickey in S4 actually realistic for a sitting DA?

In Season 4, Maggie (who’s still a Deputy DA) steps in to represent Mickey during his murder trial.

I’m curious how realistic that is in real life.

In the U.S., can a currently serving District Attorney or Deputy DA act as a defense attorney in a criminal case — especially for someone like an ex-spouse? Or would they have to resign first because of ethics rules and conflicts of interest?

I know it makes for great drama, but I’m wondering how this would actually work (or not work) in the real world.