My first thougt was also allergies. My eyes often get itchy. I swear, sometimes my brain itches. : )
Floaters and eyelashes are also worth a look. I used to have to pluck some lashes because they grew the wrong way and scratched my eyes. An eye doctor could see if it looks like that is happening & should be able to tell you if her has floaters too. Regular doc, I think, for allergies.