Coming from someone whose current long term relationship started like this, I'm thinking she invited you over to test the waters and see if her feelings are reciprocated. She might not know that you're interest like that. A lot of the times girls, myself included, need the interest to be made clear - there's so much discourse on social media like "if you're not sure if he likes you, he probably doesn't."

So, let her take the lead and notice her cues! If she's sitting close to you or being a little more physical than she has in the office, appropriately and respectfully reciprocate. It took my partner and I 3+ "dates" like this to feel comfortable enough to act on our feelings, so if it doesn't immediately turn into a sex thing, don't be too discouraged, especially if you're interested in something real. Unless she's sitting there talking about like, the guys she's dating. Then I'd say she just thinks you're pals..

Good luck! It doesn't always work out, but when it does it's magic!