I'm also going to disagree with Guinan as a magical negro:
The magical negro is typically but not always "in some way outwardly or inwardly disabled, either by discrimination, disability or social constraint," often a janitor or prisoner.
Guinan is fully abled. True, she might have had most of her species wiped out, but this is science fiction -- that happens all the time; furthermore , the Borg don't discriminate. While she plays the role of being the bar owner, which I supposed is a somewhat servant-like position, she only does this for a period of time and then goes off to do other things with her super longevities life.
He has no past; he simply appears one day to help the
white protagonist. He sometimes fits the black stereotype, "prone to criminality and laziness." To counterbalance this, he has some sort of magical power, "rather vaguely defined but not the sort of thing one typically encounters.
She has a long past. Her people were destroyed by the Borg which forced her to be a galactic refuge; at one point or another she became well acquainted with the god-like being Q. During her plight she is sucked into the Nexus; she chooses to leave, but her echo remains. She made it to Earth and manages to help out some time traveling people who will later be her co-workers and friends.
She's not vulgar, criminal, or lazy.
She does have vaguely defined powers, but so does a white female main character, Troi, and Guinan's vaguely defined powers are infinitely more useful. "Captain, I'm sensing that he's hiding something." Vs. "Captain, I think the entire time line has just re-arranged."
He is patient and wise, often dispensing various words of wisdom, and is "closer to the earth.
This does fit Guinan; but it also fits Picard and Data, as well as most of the supporting cast, perhaps again excluding Troi.
The magical negro serves as a plot device to help the protagonist get out of trouble, typically through helping the white character recognize his own faults and overcome them. Although he has magical powers, his "magic is ostensibly directed toward helping and enlightening a white male character." It is this feature of the magical negro that some people find most troubling.
When she helps Picard, she helps out the Enterprise -- which has a crew of mixed race and species. Her own mutual existence is often at stake as well in the times when she helps save the day.
To save the white protagonist, however, he would do anything, including sacrificing himself...
Perhaps. But I think this is true for most of the crew of the Enterprise-D, and Starfleet in general.