My girlfriend acts like such a prepubescent child sometimes! what to do?

I'm 37 and she's 19. I really, really love her, I would die for her. She's gorgeous, smart, y, articulate. But man.....sometimes she really does embarrasing stuff! and I am tired of continously disciplining her like an idiot. When i give her gum she chews so loudly! i give her the annoyed "look" and she stops and then continues and says, "oops, sorry"...but keeps on forgetting and blows bubbles. When I'm walking with her...she sometimes skips...and I give her the what the **** look and she is somewhat embarrased and says sorry but does something stupid in an hour and makes a twirl or spin (as if she's 9 not 19) sometimes she starts showing me funny dance moves on the street walking past security to my place....it really bothers me what the hell? so she doesn't dance at the restaurants, clubs...but decides to act like a child outside....does anyone else have this problem? Also, when we're walking and she sees a toys store she yells, "OMG!!! how cute" at a stuffed animal and I swear everyone looks at me like I'm some pervert....once i got so ticked off that i bought her coins for kids entertainment center and told her to be a kid in there and get all her energy out because I wasn't alking around looking like a pedohpile..but of course she had to drag me along! it was fun...there...but honestly...she is 19 she needs to cool it. And i am tired of lecturing her at home...I don't know what else to do...the only thing that's left is (kidding) but my hand seriously itches sometimes to her bottom hard so she acts like a lady . I once ed her at home (not playfully) while holding her wrists down in the evening for acting so immature the whole day when I was with my business friends...and she was literally crying the whole night saying she wants her mom (her mom lives in a different country)I was holding her on my lap practically the whole night...she was in hysterics. i felt horrible....i don't want to do that again.