I’m not a pro but I would advise against shaking hands, more like a soft touch on the shoulder or the arm, apologize for bothering her and say she seems like a cool girl and you’d like to talk to her. Especially if you don’t know her and don’t have friends in common, insist that if you’re bothering her, you will leave. That way, she knows that you’re safe, considerate and that the risk of you being a creep is lower. Before thinking about flirting with girls in public spaces, you, unfortunately, have to make it clear to them you’re not dangerous (not blocking their way of exit by standing in front of them if they’re against a wall for example).
If you do it like that, confidently but politely, you might get rejected but it will be kindly, and you might strike up a flirty conversation! -weirdintranslation