My cousin's bitchy behaviour - aio

I'm 24F and I have a cousin 22F, we go out a a lot. She's working in IT office. But she doesn't behave like one. Wherever she goes she plays insta reels with full sound on- I've said so many times not to disturb others but she wont listen.

Once I ordered a Espresso cuz I like it but immediately after the waiter kept it on the table she gave a Eww face which the waiter saw and he asked u ordered Espresso right...this is Espresso(She have never seen an Espresso - she thought it's a coffee with milk so she gave that face)

She did the same thing to a Pesto pasta. She wants to act Royale and tries to talk lavishly. English is our second language. Even in a parlour she tries to talk in English with a different accent but everyone else there were discussing in our mother tongue.

The thing is she gives a Eww/bitchy face whenever she's disappointed which will definitely make the employees feel irritated.

I've advised her to keep poker face if she's not impressed with looks of food(it's not that food presentation is bad. It's the first time she's seeing new foods so she should taste it first before judging it) I've asked her to behave appropriately to employees but she's not changing at all.

Im not sure if she's right or am I overstimulated and overreacting.