A risky but bold approach you can do that I've had work out in the past (albeit I always did it in coffee shops but its about the same venue vibe wise) on a few occasions is to write a text in your phone of however you would open her if it wasn't super quiet and everyone around to watch.
For example : "Hey you have an amazing sense of style! I wanted to see who you are

" or "I'm super attracted to you... are you single?"
Now you put yourselves in the shoes of someone that legitimately thinks they're phone is broken and needs someone elses opinion (that looks phone savy... i.e. hot girls who typically use their phones 20,000 times a day) to confirm that your phone is not working properly.
Put yourself in their shoes and emulate that vibe like you just need someone's opinion on your phone.
Go ask HER opinion in a friendly way and simply ask for her help.
Approach her with "Excuse me but I think my phone isn't working properly and you look like you're more expert than I am. Do you mind checking for me?"
She'll most likely respond favorably or neutral. Take note of how engages you.
Then simply slide her your phone as you say "Yeah I just can't get it too do thing X". Doing this so observers have no idea what you're really doing and think you just need help with your phone.
Carefully watch her reaction to reading the text (if you have good fundamentals you will typically never get a bad reaction from her).
She'll then make a decision about her attraction for you and either play along with the broken phone thing in a playful way or she'll change the subject out right and start flirting with you if she likes you.
If not she still may play along with the phone thing and say "it looks like it's working fine to me but thanks anyway" something like that. Or she may just thank you and tell you she has a boyfriend or tell you sorry and reject you which is fine because everyone watching can't tell the difference.
I typically write "are you single?" in the text so as to give her a way out real quick if she's not digging me (since it's a lot of pressure on her and she may fear your next move).
This works because it communicates that you understand societies pressure (you cant just go direct in front of everyone including people she may know) and you found a creative way to get around that and go direct anyway.
Try it out and tell me what you think.
-Rob