The fact that a majority of people didn't get her "joke" is a testament to her comedy skills, I'm afraid.
First, you have no evidence that any more than a very tiny % of people didn't get her joke. (Hint: the tiny % of people who respond to a particular tweet are not representative of any larger population).
Second, comedy skills are no more indicated by most people getting the joke, than musical talent is indicated by popularity (were the Backstreet Boys the most talented musical artists of the 90's?), or valid science is indicated by the majority of people accepting and accurately understanding it (Is the ToE false in Alabama just b/c most people there don't "get it"?). If anything, there is a negative correlation between mainstream popularity and talent in comedy and most art forms.
BTW, it is worth noting the objectively false reporting about her tweet. She didn't say they
were swastika's. In fact, her tweet makes it clear she knew they were not actual swastika's. She merely asked the question whether they were someone's attempt at Swastikas, and joked that if they were, then the Nazi doesn't know how to use google to get it right. Google images of "wrong swastikas" and you'll see many pics of clearly intended graffiti swastikas gone wrong. So, given that graffiti swastikas are ubiquitous, commonly drawn wrong, and that what she saw had 75% overlap with actual swastikas (likely more overlap than with other common forms of graffiti), it doesn't require being especially sensitive (just aware of one's surroundings) to have the the idea of a swastika be at least somewhat activated by seeing those spraypainted on the sidewalk.
And maybe she is more prone to see that genocidal symbol than you or I, for sound rational reasons that like most Jews with public exposure who say things the right doesn't like, she is targeted with violent anti-Semitic threats on regular basis. When it comes to perception, false positives are usually a byproduct of the system having been exposed to so many actual positives in the past. Show a person tons of pics of actual young women and they will see the image below as a young woman.
But show them tons of pics of old women and they will see it as an old woman.
IOW, just like the hate crime hoaxes are byproducts of the prevalence of actual hate crimes and white supremacist ideology, interpreting an ambiguous object as a threat is influenced by experiencing actual threats. It is there mind's rational response to an objectively high threat level to lower the threshold at which a potential threat is noticed.