Luna was wearing a black face mask and a cap that would prevent people from noticing her, so she didn't have to worry about being noticed and she just watched Mark from a distance without being spotted.
But for some reason, she didn't go up to Mark. She noticed that Mark was with Arit and Talia that day, and she didn't feel like going up to him and ruining his vacation. She wanted to know more about him before going up to try and talk him into joining her guild. So she started to stalk him.
Luna was never going to tell anyone that she was doing such a thing, and if anyone ever found out about it – especially those in her guild, she would never be able to live it down!