Women use flirting sometimes as a way to get free resources and free validation without any intention of giving anything to the person they are flirting with.

https://www.reddit.com/r/asktrp/comments/5ztpnc/why_do_women_treat_you_one_way_and_then_backstab/

Flirting is a likely thing to happen in daily life.

Flirting can also create temptation if the flirting is done wrongly. It is a known problem that you just have to prepare ahead for.

Do you, setting boundaries in the relationship, allow your woman to flirt with other people with flirty messages?

Allow means you tell her that flirting is ok.

Disallow means you tell her that any flirting from her would mean that only one person is in the relationship.