And finally, some photos taken while she was eating, post getting pinched.
I have done that in the past as well but tend to leave them alone now in terms of the pincer. I figure it is enrichment making sure to eat carefully.I break the tip off the male fiddler top claw before feeding. The fiddler often throws the claw if I am not quick enough but breaking the tip keeps me and the octo from getting pinched enough to make a hole.
Judging from the pulled "flap" on the crab she runs off with, maybe she is not injecting venom but simply using her suckers to kill the crab by separating the shell. Even the female crab you examined with the skewer after she has killed it appears to have had the "flap" pulled.