I thought your daughter’s ‘well I identify as a woman’ comment was an excellent comeback and it hoist the other student’s argument by its own petard, exposing the misogyny and the authoritarianism of their argument so effectively. Very clever.
Nobody is condoning swearing in school but your DD didn’t start it. Standard punishment only for both kids for that. Any apologies should have been required of both, although as PP have said your DD did not swear ‘at’ the other student to insult them, although she got an ad hominem from the other student.
Your DD swearily disagreed with an idea which is materially different from denigrating any person using swearing, even though you have reminded her that all swearing is inappropriate for school etc etc.
I would agree with PP’s safeguarding concern raised though. It’s important to welcome the school debating this issue in an Ethics class, this issue needs debate as there is a full blown culture war going on against women right now.
But the idea that the school might allow kids to be shut down by being insulted and sworn at if they question the dogma of genderism in front of their peers suggests the school do not understand the safeguarding risks to young people from this political idealogy and the risks and consequences for many of the young people who adhere to it.
Have they not seen Keira Bell’s ongoing court case? The letters from concerned doctors to the BMJ about the lack of evidence for the treatment of children in the NHS GIDs clinics? Dangerous binders being sent out to kids in the post by that charity in Manchester without parents consent? Concerns about lack of good safeguarding practice for protecting young people in some LGBT support groups for young people in the UK? Concerns about ostracism when kids detransition? or if they try to enforce their own personal sexual consent boundaries by saying ‘no’ to potential dates on the basis the prospective date is not of the sex that the individual is attracted to. Then the individual gets peer critique and ostracism for being ‘transphobic’, which for some young people will be enough pressure to cause them to compromise on their own consent. Are we really condoning that climate for children? Doesn’t safeguarding apply to call children, however they or the adults around them ‘identify’ their gender?
All of these issues have been posted about on here. Will the school be asking Charlie Evans’ detransition advocacy Network to Skype in for a lesson about that? (I don’t know if that’s possible or not but you get the drift.)
Don’t schools have a duty to safeguard kids against political extremism? Like with the ‘Prevent’ duty? schools should recognise that much of the movement behind this politics IS politically extremist.
Women have been punched to the ground at speakers’ corner then had to observe their attacker’s choice of pronouns in court and also have the fine for the attack reduced if they do not respect their attacker’s pronouns, women have meeting venues credibly bomb-threatened and cancelled so that they can’t talk about their own rights, and even if they do manage to get a meeting venue (labour fringe 2019) they get people trying to kick and smash in the windows. There are zero examples of this coming from women towards any trans person or organisation that represents them.
That’s not to mention losing women work, kicking them out of political parties, and expecting them to put up with rape and death threats on social media if they dare to express a pro woman opinion. There are the private blacklists of academics circulating on social media and threats made by party activists of deliberate data breaches against gender critical women’s data.
In that sense, this issue is not a debate. It’s just a sustained attack on women’s rights to name themselves, to retain their own single-sex spaces and opportunities and to speak freely in society.
None of those things infringe on anyone’s else’s rights unless you consider that the built-in rights everyone else include the right to take away from women’s rights.
^ That attitude of ‘women being less than other humans’ is SEXIST. We should all be permitted to object to sexism freely, whatever age we are. (But we accept, not with swearing if in school time 
)
Good luck! I’m so proud of your daughter, you must be unbelievably proud of her. Even more importantly, you must be relieved for her that she’s understood all of this so well and is drawing up healthy boundaries for herself and supporting her friends who are doing that. It will stand her in such good stead around all the political authoritarianism and consent and sexism issues that she will encounter as she grows up.