1) Being "not used" to racing 6km shouldn't be a deal breaker. Men jump from 5km in high school to 8km in college and nobody bats an eyelash. It literally took me only 1 race to learn to pace myself for 8km, and then a few weeks later a 10km mid October.
2) 6km being "foreign to [your] body and mind" is one of the dumbest things I've ever heard. You ran 10kms and 5kms already. You should be the most ready of anyone to race a 6km.
3) the "natural progression" for men is 5k to 8k. No reason women can't handle the same.
4) 800m runners SHOULD struggle in xc! XC is a distance event. 10,000m runners struggle in 800s all the time. Mid-D athletes need to get used to not being the best at seemingly everything in track.
5) Being used to something is not a good reason to continue it. Millions of people are used to smoking but that doesn't mean they should keep smoking.
Bonus point) mid-d and long distance runners all do enough milage to handle 8 and 10km races. The only thing holding them back is weak mental strength.