People have the right to work in non-hostile environment. If she found something offensive, her concerns SHOULD have been addressed. It's a loss for society if everyone who has ever been bullied at work had to quit their jobs. It costs the community tax revenues; it costs the employer productivity and a good worker; and it costs the employee their income. Nothing good comes out of harassing people at work. Descriminatory behaviour at work MUST be addressed, on the spot, by everyone.
Don't mythologize startups as a "non suit environment where everything goes". Suit-firms don't have a monopoly on dignity and favorable work environments. Don't sell yourselves short in your eagerness to please and fit in.
Suppose you worked at my startup. Suppose further that you suggested to one of your colleagues, as you did now, that they quit because they weren't inclined to put up with what they saw as a hostile work environment. You know who would be gone? You.
Startups are a team sport. We don't require suits, because how somebody dresses won't change the quality of the product. However, driving off perfectly good people because they're different will definitely change the product. The same applies for a culture where people don't feel respected, or aren't encouraged to fix the problems they see.
The reason I am so pissed is that I work in a company where we do things and make jokes that would get you kicked out the door in most suit companies and everybody enjoys it -- including the girls (who are often the best) -- and yes there is the guy who doesn't find it funny to change his screen, so we don't. To him. If he finds it obnoxious that we make those jokes with others, he can deal with it or leave.
And yet, if somebody where to join us who would get annoyed working there do you suggest the rest of us should leave?
I wouldn't make the joke I did in a company that didn't appreciate it but I wouldn't stand for it being change just to fit a few people either.
But someday you may hire someone who, as it turns out, does not appreciate the jokes. Or perhaps, like Jessamyn, enjoys the jokes sometimes but feels that they are overdone to the point of being irritating.
I would not advice you to tell this person "If [you] find it obnoxious [... you can] deal with it or leave." Because in the US (I can't speak for other places) that is illegal. If this sort of behavior is pervasive it is said to "create a hostile (or offensive) work environment", and if someone is fired (or effectively forced to leave) because they do not enjoy the behavior then they are well within their rights to sue your company.
I'd also question your belief that "the girls" (who are, I take it, 8-12 years old) are ok with it. Go talk to some people in the field who have had a few jobs but aren't stereotypical. E.g., gay, female, or black. Ask them if they've ever laughed at something that made them uncomfortable because they wanted to fit in and felt unsafe doing anything else. Because you're ok with pushing out somebody if they don't like the joke, guess what: if they don't like the joke, they'll still pretend to you that they do.
There are plenty of employees who like their company that way and if she didn't she is not really suited for the company culture. She can (and should) seek employment elsewhere. She will be better of there.
Finally she didn't beat them at their own game. Yes she wrote a bot, but it takes a bit more cleverness to match phrases that to simply reply to a string that is going to be the only thing that bot ever quotes.
Too bad too, since she could have made her bot do something that would have been impressive, and perhaps convince others that the bot was sexist by calculating how often the joke was mad at the expense of a male ('it is small and hard to see') versus at the female. That bot would have been impressive and it would have been a much greater hack.