I would say this whether you were male or female (or nonbinary), and regardless of her gender: go for it.
Ask, "Hey, can we get a soda (or coffee)?"
It's less blunt than a specific request for a date. You need to be a bit subtle because, like you said, you don't know if she likes girls. So you need to give her some plausible deniability.
Go (assuming she says yes). Laugh, talk, drink your beverages, etc. At the end of it, if you had a good time, say something like, "I had a really great time. Can we make the next one a real date?"
And see what she says. It might be: "I'd love to!" Or "Sorry, but I've got a girlfriend." Or "Sorry, I'm not into girls but I had a really nice time too and I'm glad we're friends." Or lots of other things. But if she's a great as you say, then she'll be kind about it if the answer is anything but "I'd love to!"
You can do eet!