I think a) it's fighting, not training, and therefore young men will be encouraged to be violent to a young woman; b) it has the potential for inappropriate touching and harassment.
So the men fighting each other will be encouraged to be violent towards other men?
And presumably the women fighting other women will be encouraged to be violent towards other women?
Or is it only when two different genders fight that you consider a martial arts competition to be an encouragement towards violent behaviour?
With regards to inappropriate touching, they're grappling, not copping a feel. Assuming your daughter is fighting someone of equal skill, if they try to grab a handful of ass or boob then they'll very quickly find themselves locked and tapping out. You don't have the leisure to have hands wandering at will when you're fighting someone. Plus the judges, spectators and other entrants will take an extremely dim view.
With regards to harassment, most trainers are extremely fast to tackle anything that even remotely looks like sexism, because women make up a high number of their clients, and they stand to lose large quantities of money if they alienate them, to say nothing of being decent human beings in the first place.
YANBU to worry, but I think that's gut emotion, not logic, speaking.
You would be extremely unreasonable not to let her take part, or to do anything other than encourage her in her sport.