I want to roast one of my cousins on her birthday next month. What are some good roasts?

She’s turning 19 and I wanna roast the hell outta her and humiliate her! She should know that we’re just joking around so she shouldn’t get offensive. I like to joke and I’m very sarcastic in a good way. I need some good roasts. None of the easy, childish comments. She’s not a child anymore so she’s old enough for adult jokes.
Plus she’s very tall (6ft) and broad.