Thank you so much, guys, for all your thoughtful comments and your sensible advice, most which recommends doing nothing at all and quietly enjoying the encounter.

I understand perfectly. And yet I think what could be possibly wrong about approaching her and saying: "Excuse me. You´ve got the most incredible long hair, it´s incredibly long and it´s absolutely beautiful, too. Please never cut it. Have a wonderful day."

If that were all I would say to her, could that still come across as creepy?

I´m not standing next her drooling, I´m not staring at her wide-eyed, I´m not desperately hal-hiding behind shelves trying to take a candid photo. I don´t want to take a picture of her and her hair (actually, I would want to do just that, but it´s clear to me that that is an absolute no-go), I don´t want to touch her hair, play with it, have sex with her, let alone get a hairjob. I really don´t.

I just want to compliment her and make sure that her effort at growing her hair that long does not go unnoticed and is sincerely appreciated, too.

Wouldn´t that be a decent enough thing to do?