My [19M] girlfriend [19F] requires to comment on her instagram posts

I made an agreement with my girlfriend (without really having an option) that any time she posted a photo on her Instagram of just her, I would be required to comment something silly like “love you😍” or “gorgeous.” She has been clear that this is important to her, but i think it’s very childish, especially considering I hardly use social media at all. I’d be more than willing to tell her how pretty she looks, but not out in public in this medium. It seems like she wants me to do this only so other people know what I think of her. I don’t believe this should be a requirement. Is it unreasonable to feel this way?

TLDR: My girlfriend makes me comment affectionate things on her instagram posts and I think it’s weird, am I being unreasonable?