Sorry you were not aware of TGIF's policy. Way back they hads "No Concealed Weapons Allowed" stickers on their doors. Then they changed to "No Illegal Guns Allowed". They must have figured out they screwed up the signage and are now just supposed to enforce the policy at the door.
Kudos on being willing to get up and leave with food still on the table. (Much better to leave it there than to ask for a box to take it with you. Makes it harder for management to insist you pay for what you do not get to eat.)
More kudos to the daughter for taking on the manager in a polite, rational way.
Play up the personal embarassment issue when dealing with management (GM & higher). Refuse to accept gift cards or other concilliatory offers, stressing that besides not wanting to support a place that fears inanimate objects you would not want to return to the site of such distressing treatment. Heck, threaten to sue them for emotional trauma if you think they would care.
A "one-time exception"? Either it's a policy or it's not. I know they'd like to avoid a scene, but I have more respect for someone who stands by their policy than someone who waffles before the almighty dollar. (If you are a halfway decent manager you know how to get someone out of the place without a scene ensuing. If you are a decent manager you should be able to do it without anybody else noticing it.)