Just go in lower energy, I usually wouldn't use a "totally cute" opener in that case, but you can certainly compliment her on something she wears etc. Just keep it deniable, like until you get her out on a date don't say things that are explicitly sexual or convey too much intent, make sure everything has a double meaning. A better question would be, "if she's in my classes then should I ask her out on a date, what if things get awkward?" and that's a call you have to make. Sure, there's a girl like that in my office, but hey, who cares, I acted like a dick (got nervous around her, etc) and made things awkward and uncomfortable but IDGAF...
-Ray