It is generally allowed if one appears in court and seeks permission to do so. As my comment stated, this is called making a “pro hac vice” appearance.
I find it curious that Allred frequently flies into a location outside of California and appears in front of a microphone and announces that she is representing someone. Of course, given her ego and the media’s lack of attention, no coverage is given to her local co-counsel, if any exists. Moreover, in numerous cases, no lawsuit actually results. It is all about Allred getting camera time or pushing her political agenda. She is a Democratic party activist after all.
Interestingly, the California State Bar is investigating Allred. We will have to wait and see if any discipline is imposed.