I don't understand, TPR advocates both setting boundaries and no mate guarding. They are contradictory.

For example, I recently lost my GF to a guy who was one of her long term text buddy/obiter.

She just said, if you are not coming for dinner than I'm going to have dinner with a friend. Then I asked which friend, she said a guy from a party, which she has been texting.

If I tell her that she shouldn't go to the dinner, then I'm setting boundary but mate guarding.

If I tell her not to do to the dinner, than I'm not setting boundary and not mate guarding.

This is really confusing.