Alex,
... is there any way to delete that one post? Or maybe better yet, edit out the offensive content?
Both options should be available to you (as a mod/owner) via the More menu:

If you choose to edit the message be aware that you'll have the option to resend the edited message to the group or not; but it will be emailed to the original poster (you don't have an option about that).
I did find where I could delete the whole thread but, oddly IMO, I was unable to find a function that would allow me to delete the one offending reply/
A moderator might not have those options, see the Edit Archives permission in each moderator's list of permissions. But having that permission should enable both editing/deleting messages as well as topics, so that wouldn't explain why you see one and not the other.
Shal
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