Originally Posted by
corrado33
Maybe she's back pedaling when cross chained and ripping the derailleur off? But that wouldn't explain the missing pulleys.
That was my thought, too. That's theory 1.
My only experiences with losing an RD was when I worked in the bike shop and didn't set the low gear RD limit screw correctly. The buyer shifted the RD into the spokes and that was that. This also aligns with Corrado33's experience. Theory 2 would be low gear RD limit misadjusted.
Theory 3 would be the high gear RD limit screw misadjusted and the chain getting caught between small cog and frame.
Theory 2 doesn't jibe with the claim that the breakage occurred whilst shifting to the small cog. As for theory 3, I can't figure out how that would result in cage and jockeywheel loss.