It could be argued that the message itself was dismissive of dialog, which is counter to the 1st Amendment freedom of speech. It is not as though it said “Some people are gay. Let’s talk.”
Keep in mind her response was “it’s a tee shirt and it’s not hurting anybody”
That’s an and condition. The fact that it’s a tee shirt of objective, but it not hurting anyone is subjective.
IOW tee shirts with messages that “don’t hurt anybody” (subjective judgement) are ok. Tee shirts with messages that DO “hurt”’someone are not ok.
Effectively she’s indirectly engaging in and promoting suppression of speech and thought. Would love to see her reaction to someone wearing an anti-gay tee shirt. She’d probably claim she was emotionally distressed (”hurt”) by it and demand official action.