Why does the morals champion always become the target for corruption? I mean, it makes perfect sense for the fetish to be applied there. Black ink stains brightest on white paper. But still.
If it really was what she thought, she needs to be more assertive when declining if she truly wishes to decline. What she said is too easy to take at face value and reply with how she wouldn't be in the way and should just join in on it.
Oxytocin is not just for bonding between partners, but with so called in-groups (family, friends, etc.)
An unpleasant side effect is that it makes people wary of people who aren't in that in-group. Foreigners, people who are not like you or the people you surround yourself with.