Jump across to the first platform and grab the three bottles there, then climb up to the rooftop. Take out the card thrower up there, then grab three more bottles before jumping across to the red pipe and climbing up to the next roof. Here you'll run into Carmelita and you'll have to spend the rest of the level dodging her stun blasts. Jump over to the roof on the right and take out the safe and the three bottles. When you have them, use the mattresses to jump up to the spire and take it over across another spire to the next roof. There's another safe here and two more bottles you can get before using the mattresses again to get up to some more spires. These will take you over to another rooftop, and from there you can jump down a series of roofs until you get to a bigger area.
Break open the safe and grab the bottle, then use the mattress to jump up to the clothesline that takes you to a couple planks leading to another roof. Grab the bottle there then jump onto the next clothesline, which breaks, making you climb up to the next roof. Grab two more bottles here and jump down to the checkpoint below where Carmelita can't shoot at you. Grab the bottles here then head through the doors and smash three more. Go down the hallway and take out the card thrower and you'll find yourself back in the casino. Go between the two guards' flashlights to get around behind the one on the right, then take him out and the safe behind him. Use the mattress to get up onto the spire above where you can cross the lights and drop down onto the other guard. Break open the safe he was guarding then you'll have the code for the safe right next to you.
Use the mattress to get up to the lights again, but this time continue on. Jump down to the tables and Carmelita will show up again. Keep running and jumping across the tables and walkways to keep ahead of her gun blasts. At one end you'll climb a ladder and go back the way you came one level up. At the other side you can climb up to the top of the structure and start back the other way again. Use the mattresses to get up onto spires and platforms along the way. At the very end you'll need to break open the key case, which takes a few hits, so be sure to jump out of the way if she shoots at you. When you break it open, it also breaks the anchor of the balloon Carmelita is standing on and she'll float away.