Our Commander in Chief has been known to give out derogatory nicknames to those in the capital that he doesn't like very much. EG: "Pocahontas" for Elizabeth Warren, "Crooked" Hillary. I mean, for goodness sake's, there's a Wikipedia article with a comprehensive list of Trump's mean nicknames and who they belong to.
While Wikipedia does include names used on Nancy Pelosi, all of the nicknames still include her own name, Alexandria Ocasio-Cortez doesn't even make the list. While the internet has adoringly dubbed her AOC, Trump himself hasn't felt the urge to demean her with a nickname.
So, what gives? Why do Pelosi and AOC get spared the derogatory nickname?
(Also, remember that in no way is this normal.)
I may be making a giant assumption, but it seems to be, that Trump's nicknames are meant to demean and belittle the receivers of them. So, by giving both Bernie and Hillary nicknames during the course of the election, he associated them with those traits and demeaned them in the public eye.
Nancy Pelosi and Alexandria Ocasio-Cortez aren't people that Trump can easily belittle. The reasons for why are varied and speculative, but it seems that Trump has found these to be more difficult to harass in front of the public. It could be because of mass public support for them, but Bernie Sanders and Hilary were both moderately popular in the eyes of the media and general citizenship.
In my mind, that narrows it down to two things. Either Trump does not view Pelosi or AOC as threats, or... he is afraid to nickname them.
It seems insane that Trump would not view the two as a threat, given their very public statements regarding his policies. Pelosi and Cortez are threats, but big enough ones that Trump is afraid of their retaliation in the political scheme, and therefore, it's too dangerous to give them nicknames.
But now we can see through him. If he can't demean these two strong women for his own political gain, what can he do?