Flirting with an employee as a 'customer'

Hi,

I was hoping to ask for some advice to approach this girl.

I first saw her last summer in a class at university. We sat near eachother but I only made an effort to talk to her once - so she knows who I am. She was very cute but shy. I wish I had talked to her more. I guess I'm pretty shy too until I get a rapport going.

Funny enough I've seen her working the till of a cupcake shop while on my way grab coffee.

I hate the thought of hitting on an employee... but I thought of saying hi.

Should I just acknowledge seeing her from the sidewalk, buy something, ask how school is... etc?

I wouldn't mind asking if she'd like to grab a coffee, but I don't want to be a D-Bag.

Have you been in a similar situation? Please advise.